Where are those files located? I think I'll jack with them a little.
Such evil thoughts

Look under the Twighlight subdirectires in the "Program files - Stardock" part of the disk. You'll see a multitude of them - all over the place. Do NOT mod an inplace one, if you want to mod one, make a copy, do the changes, then put the altered one into the "Mods" folder, and most important
leaving the original in place. Then check mark "use mods" in the game options screen. The ones you are looking for are those with ".xml" extensions
Be
very picky with yourself on this, else you will as sure as night follows day end up forgetting you changed one, and you'll wonder why something is happening. The main reason though, is when an update happens, original files in the main directories can be overwritten by the update destroying your modification, the MOD folders are left untouched. Always, always, always, keep separate copies of heavily modded files on a removeable storage media - lots of effort can go into these (small simple changes are easy) and its a bummer to loose hours/days/weeks of work when the disk crashes ......
On my PC the directory for the file dealing with the config of Homeworlds is:
C:\Program Files\Stardock\TotalGaming\GalCiv2\Twilight\Data\English\CustomPlanets.xml
The modded file (leave the original in place) goes into:
C:\Program Files\Stardock\TotalGaming\GalCiv2\Mods\Default\
Below "default" in the MODs directory are a series of sub directories for specific modding files, I dont bother as I have no need with my simple tinkering. The Modding community will lead you on the proper use of those.
Never touch the ones under the Metaverse Directory, they are exclusively used in the Metaverse games, meticulously checked for illegal modding, and will result in a cheat flag appearing in the respective Metaverse game record if they are changed in any way
There's a thriving MOD community here who do doubt will launch copious "welcome to the true way" statements hot on the heels of this reply. There's also a thriving MOD forum section here
I just tinker around the edges of modding for a bit of fun, those guys do it for the survival of their Souls
Regards
Zy