As far as I know you don't get your spells back nor get healed unless you are fully rested.
You do, if you pause the game before you rest. That may be an exploit but still...
Anyway, for fun try it in a city area a couple of times and watch 10-15 Amnish Centurions spawn arround you while you happily rest and regain your spells.

Another *area* you could look at is to disable the rest button itself, using IEEP and choosing <Disable Buttons> (it can disable spell, talk...) but I am not sure about the *rest* button though a lot of buttons nos are unknown
Just tried this, but the 'Rest' button doesn't show up on the list. I tried some 'unknowns' too but that didnt help either
BTW, I'm sorry if my earlier reply came of as a bit rude. It wasn't directed against your comment specifically, but rather at the apparent inability of the
IE to do something as simple as make an area 'unrestable'.
I mean, that is a very basic feature for
D&D cRPGs, and one would think they would have a simple 'rest/no rest' flag in the .ARE but noo...I have to find a workaround even for that.