I basically want to be able to make my clerics use bows, my wizards swing axes, etc. Is there a mod for that? Can I just give that epic thief ability Use Any Item to every character?
Thanks for your time.

You can give the thief UAI ability... I recommend to do that with ShadowKeeper. That doesn't give the mage the ability to gain proficiency points! Ah, well, you can edit them too...

Or if you wish to make the change with mods, Ashes of Embers should give that, Level 1 NPCs should contain a component for that...