That was easy, though there is one slightly annoying side effect.
I didn't have to mess with scripts at all--just go in and change what the "Transform no Spellcasting" spell that's applied whenever you shapeshift does. Setting a Sound effect up to 500 makes casting anything else impossible and still allows you to cast Cancel Transformation to get out (unlike Silence, which says you have a 100% chance and then keeps giving you a spell failure message).
The annoying thing is that it constantly plays the "
whisperwhisperwhisperwhisperWhIsPeRwHiSpErWhIsPeRwHiSpErWHISPERWHISPERWHISPER" sound effect the whole time you're transformed. :swear: The changed version may be from a mod I have, though, as I don't remember vanilla Sound spells being that obtrusive.
*test*
Yeah, if you're using Lucypher's Magic Sound Effects Replacement and want to implement this, I suggest you go in and rename the "Sound" spell file under Data Files/Sound/Fx/ if you don't want to go insane. Other than that, it seems to work perfectly.