I... have absolutely no clue what you're trying to do here. Eyes don't have GUID numbers, they have instance numbers. Technically similar, but Bodyshop handles making new ones just fine.
If you're trying to work around the weird texture saving in Gimp, the easiest method is to make a new eye project in Bodyshop, re-use the project several times by doing "import to game" without changing the textures (the new files appear in SavedSims, don't use or do anything to the Package files in the Project folders). You can make the textures (export as PNG files) in Gimp, and you can then replace the textures in SimPE.
It's perfectly safe to re-use projects in Bodyshop, and every file will get unique instance numbers.
I use this method a lot, particularly when making infant outfits (I make the textures, count how many I need, make a recolor project in Bodyshop, and do "import to game" as many times as I have textures. Then I replace the textures and do various other changes in SimPE, before I compress the files with the "Compressorizer" program to save disk space).
That's what I meant though. I already did all of this and I made six eye colors fine, what I meant to say is that they all have unique instance numbers, GUID was probably the wrong word to use.
EDIT: I'm now marking this as solved since I figured out how to do this correctly. I still plan on doing a tutorial sometime in the future.