I'n another thread, I got asked...

But rather than derail a thread I wanted to progress on topic there & felt like giving this a proper justified it's own thread.  In short, I cheated by doing a pretty extensive mod in galciv2 (reading that & the wishlist at the bottom again & playing with the GalCivIII xml's makes me grin with glee!)

On That note, I feel like The question deserves a proper reply involving a tutorial of sorts 

Tetrasodium's guide to Modding GalcivIII

The Basics.

Almost any setting/configuration in Galciv II & III can be modified through direct modification of the xml files, including those with no way to modify them through the interface (even if just currently the case).  You can simply open them in notepad, save some changes, relaunch the game, & start a new game (copies of xml files are saved within the saves themselves).  On an interesting/debugging note, I've noticed that as of 0.61 it was possible for somechanges to the xml's to be reflected immediately in the ship designer (specifically I added a ShipRange multiplier for cargo modules & started adjusting it I don;t know if this is just the tip or if this behavior will change/remain). I'm not going to note any graphical/ui related xml's though... that's a whole 'nother ball of wax

• Most (all?)of the text for anything you read in the game can be found in data\english\text, but there are notable exceptions such as most/all of tthe tech tree descriptions & briefing texts that do not currently appear to be in an xml file... I have no idea where it is or why an XML file with stats will have a ShortDesc/Description/Etc that gets defined elsewhere in a linguistically localized flavor text elsewhere in GalcivII, I haven't found most of them in GalcivIII yet.
• AIStrategyDefs.xml: I have not figured out much on this yet & don't think anyone ever made mods to it in galcivII either, but it sets up AI strategies based on tech ages.  I have some suspicions on TurnLifetime, TurnStart, Spending, & to a lesser degree "Weight", but have no idea how many of my changes caused things to hang from my errors or work in progress beta build 0.61 AI.  I can remember threads about it on GalcivII's forum where would occasionally ask & get told that there was no known details & it was a very complicated black box.  Since the current 0.61 AI StrategyDefs.xml file is pretty basic, this copy of the 0.61 version of itmight come in handy to someone later from now.  I'm hopeful that one of the stardock folks will give us some more detail on it though 
• [RaceName]TechDefs.xml: This is where all of the items in the tech tree (not the things they unlock, only the things you research) along with any instant bonus's you get from researching them (I.e. +1 diplomacy, +10% whatever, etc).  Each Race has their own version of it.  Yje flavpr text appears to be in data\English\[Racename]\TechDefsText.xml
• TechDefs.xml: In GalcivII this was where every race had the shared tech tree, I have not tried to see if this is used anywhere, or where if it is.
• StatTypeDisplayDefs.xml: I think this is UI related
• StatTypeGroupDefs.xml:  I'm not sure if this is what it looks like, but I think it might define what attacks what (i.e. lasers/shields, missiles chaff/etc) and maybe grant the ability to add a fourth or hybrid type of weapon/armor... that or crash the game(?)
• StatusEffectDefs.xml: Most of the things in here appear to be not fully implimented (if at all) as of build 0.61
• StellarObjectDefs.xml: not sure, believe it is involved in star color & such
• StrategicIconDefs.xml: the wire frame zoomed out ship icons?
• StrategicResourceArtDefs.xml: a related UI thing?
• StrategicResourceDefs.xml: Since these guys are on the list of things the devs are still baking & strategic resources are in their infancy as of 0.61 (at best?) I'm just going to say "it involves them"
• TechAgeDefs.xml: this file defines were you cross into a new tech age & those affect/unlock certain things keyed to tech ages. 
• TechSpecializationDefs.xml: I think some of these were in the earlier mentioned techdefs.xml in the last game & I've yet to find the xml file that contains the descriptions it links to.  I'm just going to say "I'm not really sure"
• [RaceName]TechSpecializationDefs.xml: see above
• TileAreaDefs.xml:  I have no idea.. ui related?
• TradeRouteDefs.xml:  appears to define how trade routes generate income, the number of trade licenses used, etc
• TreatyDefs.xml: defines text of  treaties (I've not found it's xml file either), their requirements, benefits, etc as far as I can tell
• UIColorDef.xml: a UI file obviously
• UPResolutionDefs.xml: This does exactly what it says, what UP resolutions are choosable, how the ai views them, & what they do.  Want to add some more UP Resolutions?... Find one similar to your idea & simply add bits from other resolutions (or modify the stock one) to achieve your idea. I do not however know where the tedt of the resolutions themselves are kept
• AnomalyDefs.xml: Defines the anomalies that survey ships can survey/investigate.
• AsteroidDefs.xml: Mining isn't really complete right now as of 0.61
• BattleBehaviorDefs.xml: Interesting looking file that appears to provide rules on how ships approach each other in combat, their target selection priorities, & their  engagement ranges.  combat is a work in progress though with little details making this extremely interesting
• BorderArtDefs.xml: UI?
• ColonizeEventDefs.xml: This contains all of the colonization event definitions & what they do.  It's the place you would go if you want to add more/modify existing ones.  Their text is in data\English\ColonizeEventText.xml
• ComponentClassDefs.xml: involved in ship components either mechanically or in a UI/logic manner
• ContinentDefs.xml:  Ever wonder why a class N world has Y tiles... yea this... that  & more (?)
• Cosmetic.xml: UI
• CultureTraitDefs.xml: Think there should be a culture trait for X, or that a given trait should have a new effect/value, go here.  Also the number of culture points you need to buy it
• CultureTreeDefs.xml: This is where you set what tier of the tree that each trait is on, how many from the last tier you need to move on to the next, 
• CutsceneDefs.xml:  Cutscenes .
• Diplomacy*.xml: Defines various aspects of diplomacy options
• DiplomaticActions.xml: Defines how the ai views some of them?  
• DiplomaticModifierEffectDisplayDefs.xml:  lookEncounterDefs.xml:s like this is either the min/max relations that an ai will do/accept a diplomatic option... That, or the min/max it will take relations(?)
• DiplomaticModifiers.xml:  This appears to be the numerical values of how various  things affect relations (shared borders, trade, tribute, etc)
• EncounterDefs.xml: Work in progress(?)
• ExtremePlanetDefs.xml: Work in progress(?)  the effects on populations/construction/etc that extreme planets have perhaps?
• FactionDefs.xml: The details on the different factions, which perks they start with, names, picture, colors, etc.
• FlavorText.xml: The text for the $Race1 to $Race2 greeting blurbs
• Formations.xml: appears to be positional formations for ship fleet formations.  Unknown use
• FXBsttleViewer.xml: *shrug* graphical effects/UI?
• FX*.xml:*shrug* graphical effects/UI stuff?
• GalacticEvents.xml: The various Galactic events & their events, I do not know where their flavor text is though.
• GalaxyDefs.xml: The details on how the various galaxy types  are dispersed(?)
• GalaxyScreenArtDefs.xml: ui/visual  effects?
• GalCiv3AIDefs.xml: The modifiers given to the AI at various difficulty levels
• GalCiv3MapDefs.xml:   Defines various star dispersal details.  I'm particularly partial to changing educeStarSystemBoundarySize to 2 as the current setting was admitted to be wider than intended.  A 2 will place neighboring stars close enough to share starbases sometimes.  A 3 will  do it less often.
• GovernmentDefs.xml: Work in progress, appears that it will define the effects from various government types
• GovernorDefs.xml: Appears to Give the priorities for the currently disabled colony governor options given various planet qualities.
• Ideologica;GalacticEvents.xml: Galactic events basedon ideology?  The flavor text location is unknown...
• ImprovementDefs.xml: All the effects of The structures you build on planets.  The text for them is in data/English/ImprovementText.xml
• MapSetupDefs.xml: Appears to relate to dispersal of doodads in space
  
  
• MapSizeDefs.xml: swtails on how maps of different sizes are built & their modifiers, however it appears that <GlobalCombatMods> is very limited in what it allows. opening that up to multipliers for more things would make major mods a little easier.
• ModifierTargetTypeDisplayDefs.xml:  Beats me/ Logic/UI related?
• NebulaDefs.xml: They are disabled in 0.61 still & their function is relatively unknown/vague.
• Pathlines.xml: Appears to involve the visual path lines ships & planet/starbases make(?)
• PlanetTypesDefs.xml: I'm not really sure, but related to the things you build on planets
• PlanetArtCategory*.xml: Artwork stuff
• PlanetaryProjectDefs.xml: the stats for projectslike cultural festival, economic stimulus, assembly, etc.
• PlanetDefs.xml: The  stats for specific named planets (Iconia/earth/drengia, mars/saturn/etc).
• PlanetFeatureDefs.xml: The stats for things like Geothermal Springs, Planetfall, etc.
• PlanetTerrainDefs.xml: The stats for things like grassland, mountainous, etc
• PlanetTraitDefs.xml: The stats for traits applied to planets themselves (i.e. 50% influence/25% manufacturing/-25% growth/etc).  Yjrir FlavorText is in data\english\text\PlanetBonusText.xml it looks like
• PresetGameSettings.xml: they Have to be stored somewhere, why not here?
• PresetMapSettings: see above
• RaceTraitDefs.xml: The Bonus' for the race traits, the descriptions can be gound in data\English\RaceTraitText.xml
• RadialIconHUDDefs.xml: UI/VFX related?
• RelationsPowerDefs.xml:   Related to diplomacy, not sure how effectively this can be modded
• ResourceDefs.xml:  Uhh... "ZombieHipsterFlesh"?....  Work in progress?
• RiftDefs.xml: some details about unfinished rift feature's configuration
• SceneLighting.xml: ui/vfx related?
• ShipBlueprintDefs.xml: appears to be related to how the game knows to call a ship things like a sniper, bomber, etc
• ShipAugDefs.xml: No idea
• ShipClassDefs.xml: appears to be a few specific ships, perhaps lostWhatever's? if not... no idea
• ShipComponentArtDefs.xml: Defines the artwork for specific ship parts.
• ShipComponentDefs.xml: The specifications for the individual ship components (engines, weapons, life support, etc).  The flavor text is in data\English\ShipComponntText.xml
• ShipDefs.xml:  More specific ship tempates.
• ShipHullDefs.xml: pull everything off a ship hull, this is what defines the model
• ShipHullStatsDef.xml: this defines the base hull stats to go with it.
• ShipMovementDefs.xml:  Beats me, logic/vfx related?
• ShipYardDefs.xml: Not really sure, maybe it's a work in progress for shipyard upgrades given it's limited details
• StarArtDefs.xml:  Star artwork... defined.
• StarbaseDefs.xml:  Looks like the kinds of bonus'  given at that work in progress above?
• StarbaseModuleDefs.xml: details on specific starbase modules
  
  
• StarSystemDefs.xml:  Details on specific planets..
• StatTypeDisplayDefs.xml:  Looks tooltip/ui related?
• StatTypeGroupFrgd.xml:  Not sure

With that said... Keep in mind that people who puut together changes for xml tweaks tend to enjoy feedback & often find it encouraging.  Given the message below that loads every time we start the game...  Fire up the braincells!