I know zilch about aerobatics but I thought that most of it is done at mostly constant-ish power settings...
If there are large power changes involved then I don't know how you can protect the engine.
The rule I use for flight tests (my own; I am not an instructor) where e.g. a PFL or unusual attitude recovery will be done is to fly at 18" or below (120kt in my case) for a couple of minutes. That gets the CHT down to about 350F.
16" may be even better; that roughly corresponds to what you fly a reasonably steep final approach at, and obviously you always close the throttle after that
