But since we're doing this mostly for GCCG, isn't it possible to change the text of the cards? Like with Photoshop or something like that. I know that it's possible and that it's not really that difficult to do, especially to someone who knows that stuff, but I am not sure if we are allowed to do that (concerning legality issues). If someone who is more knowledgeable about legal stuff could assure us that it's safe to do that, then I see no problem.
CTRL+H does show the errata text, but if that is still "too difficult" for players, it is easy to update the images. I've actually done this myself for GCCG on my computer for all the existing cards with errata...
Gimli, DoE,
We Must Go Warily, etc. I've also made generic card inserts for them for real cards. It was really easy and eliminates the need to remember anything. So that part of it is not a problem. The only potential issue with that is if anyone would really care about changing the image as long as it is just on GCCG.