I've done a bit of tinkering with LI1's save formats, by opening them in HxD and doing file comparisons and the like. I haven't done a whole lot, but it seems fairly basic, so I'll just post some of what I know here, at the very least to get some other people interested.
Player names are obviously stored in Players.gsi, but not as text - rather, with values like 00 for A, 01 for B, 02 for C, etc. and 00 between letters. There's some other stuff in there, but I haven't messed with it much.
Each player's name has a corresponding G#.GS file - G0.GS, G1.GS, G3.GS, etc. Open one of these and you'll get some basic config stuff followed by a bunch of variables - again, I haven't looked into it much, but I do know that eighth value in the file controls the current character you're playing as, and at the very end of all the other stuff there's two things that can easily be edited very easily: the sky color (I was able to edit these and change the color manually without trouble never mind, it's weird and glitching out on me now, default is 56 54 68) and the light position (just a single digit, and of course it can be altered in-game as well via observation deck controls, like the sky color).
Of course, there's a ton of other data in there which I haven't messed with - stuff that saves the customizable aspects of the game, what missions you've done, your scores, etc. If somebody else wants to look deeper into all that, be my guest - I imagine most of this could be figured out quite easily by comparing two game save files that are identical except for one thing, then narrowing down what changed between the two files (that's how I noted which value controls the current character, simply do the same for other values).