<Butting in>I would say that an Italian irregular verb could be defined as :- Any verb that uses {{it-conj}} directly, or that uses any of the other it-conj-... templates with one or more overrides specified (i.e. other than the 1st (stem) or 2nd (helper verb) parameters.
I don't own it. It was one of the very first Lua modules written and is probably not very efficient. (Though I doubt that I will be able to understand it after you have modified it!) Just as long as all the it-conj-... templates continue to work, I would have no objection (I assume it will be properly tested).
I've started working on it a bit. I'll try to keep the errors to a minimum, and I'll be monitoring the script error category to make sure. Please let me know if you spot any mistakes in the tables.
I have a question, though. The "over", "wiki" and "alts" functions that you wrote are exported, but are they actually used in any other modules, or only in this one? If they're only used in this one it should be safe to un-export them.