"This is quite sucky though, I've never seen a game where you couldnt use your savegame after a patch."

Actually, the patch will fix the resistances retroactively. There is no need for any hacks to do so.
Some of the story fixes and changes in the patch only apply to new games, but the technical fixes and changes work for previous saves.

There was a bug with removing a piece of equipment with a Magic Barrier bonus if you had not already learnt the skill.

The save editor topic also has a working download link to a zip file.