If it includes the option to name a star system they have to finalize that aspect of their code at some point. While naming a star likely just means a line item in a text file that file has to be "completed" to prep for distribution of the game.
It sounds like you touch on the idea in your second sentence... but assuming the developers have have a clue about how their programming this (and they have to, given that they're working with code *way* beyond anything I'd want to touch -- I hate 3D engines) then any 'resource', be it a 3D model or a list of star names, will be in it's own, external file.
Adding a new star name to the list should be easy, something that can be done continuously. Don't forget, one day they'll release patches, too!
That said, I'd expect the sales to be cut off around the time the beta rolls around. No point in offering beta access then.