Is there a way to just mod the Terran Alliance to use a custom symbol graphic instead of the default Terran Alliance symbol?

I tried a custom race and picked everything the same as humans but with a new symbol, but then I got a sun named "Earth" and no Mars, Jupiter or Saturn. I tried naming the homeworld "Sol" figuring I could rename my home planet to "Earth" but then I still don't get Mercury, Mars, Jupiter and Saturn. (They get named "Sol II", "Sol III" and so forth.) I also got a different robot character that I don't like.

Any ideas? Is there maybe a way to create a custom race that will use the Terran Alliance for everything including starting solar system, robot character etc, except for those things I specify such as the custom symbol graphic?