I've modified once in 2004 all 3 main ESMs in Polish verion of GOTY. I fixed this way typos, bugs in scripts and dialogs, untranslated or misnamed cells, and results were satisfactory. However, it required an update to all mods with changed size of ESMs, and change the cell names in mods depending on the original with typos or those untranslated. This also involved patching English->Polish plug-in converter with updated cell names. I needed to use a hex editor for changing some things.
IIRC, the only texture fixes were only changed file names, but I haven't tried to 'Texture Fix' what was embedded in ESM though.
Since I bought English version of the game, and started to use it instead of the Polish one, I haven't done the same to it.
So, yeah, the distributability would be my main concern. I suspect you're right about that (unfortunately) .
What would it need so these modifications could be redistributed without enormous size of file and legality problems?
- A differential patch and a patching application that would apply the patch to ESMs.