[Powers] Regeneration only on inactive Alternate Form
 

Regeneration on p. P70 has a Limited that accelerates selected advantages, such as Unkillable 2 and 3 HP regen only while dead, and DR only regen. This is valued at -40% for each [Advantage] Only.

Would it be fair have something like Regeneration (Inactive Alternate Form Only) if you had one or more Alternate Forms with Reciprocal Rest and Non-Reciprocal Damage?

The idea would be that the inactive form(s) healed faster, but only while inactive. Switch to one of them and that Regen no longer heals that form, although it will heal the previous form you were using.

I guess some questions are:
- Should this be allowed at the "character level" (so it affects all inactive Alternate Forms like this) or at the template level of each AF as desired, or are both potentially okay depending on what your goal is?
- How should it be priced? Is -40% a reasonable value? Or should it be more or less?

Re: [Powers] Regeneration only on inactive Alternate Form
 

I would say yes definitely allowable.
Especially since higher levels of regeneration are most useful for combat.
I would probably base the cost using Accessibility. So figure out how often your going to be using that form or having it rest up.
Also the discount depends. Buy it as part of the AF and its worth more but buy it as part of the character and it carries over you would think it would be less. However that would not actually increase the cost of each AF.
With that in mind I think 10% (the difference between AF and the base form costs) is appropriate for powers like that.

Re: [Powers] Regeneration only on inactive Alternate Form
 

Hmm... It seems more like a limited form of the Reciprocal Rest enhancement, since that is what is allowing the healing for the inactive form.