Not sure. So far it breaks the script extender (F4SE) so it breaks the mods themselves, but you might be lucky in your case if it’s already baked into your savegame.

Depends on the mod, I’d generally assume it’s an issue unless the mod author says otherwise. The more the mod touches, the higher likelihood it’ll be an issue.

That said, Fallrim tools does include resaver which I have used in the past to rescue Skyrim saves. Obviously backup before trying, worst thing it doesn’t work so there’s no issue trying