Modding forum tends to move pretty slow. That said I have no experience looking at save games.

Thank you Kareal, i'll keep coming back here to check on the post from time to time then.

So far, even modifying the slightest word: Terran to Lava for example, makes the whole game corrupted.

Changing the custom race stats works, but then the game forces you to change them back when loading.

I tried making the starting race have a strategicresource1 on a new game then changed it to strategicresource2 when I found the planet through descriptions, but this causes the corruption too. No idea, at the moment i'm just perma restarting until I find Jade/ Trans nearby, which hasn't happened in the past 59 attempts >>

I'm not super experienced with what you're trying to do, but I think I can help with a few pointers at least:

So far, even modifying the slightest word: Terran to Lava for example, makes the whole game corrupted.

This is probably due to the save referencing the same objects in different parts so if you modify a planet type from Terran to Lava... chances are it's still a Terran somewhere else, thus corrupting your save.

Basically, text-editing a binary save file is rarely a good/viable idea (hence why some other games have two save options: Compressed (usually Binary, fast but hard to edit) and Uncompressed (slower but editable via a simple text editor).

Another option (I haven't tested this myself so it's mainly an educated guess) would be to edit the save via a binary/hex editor but it's much more complex and you pretty much have to know what you're doing.

I hope this helps :)