Re: Can you choose not to Regenerate?
I can imagine sadistic-villain constructs where Regeneration with Always On could be exploited to the hero characters' detriment (especially if coupled with the bleeding wound rules), but they're custom nemesis sorts of things, not enough to merit Always On as a limitation worth anything.
Example: Growback Boy and Somethingelse Lass get captured by Dr. Wicked. Both end up shackled in the same laboratory. Somethingelse Lass is obviously wired up to Wicked Electrodes. The switch for the electrodes is a photocell, so that light shining on the photocell prevents the electrodes from operating. Photocell is put behind Growback Boy's left thigh, which a minion of Dr. Wicked then lops off with an axe.
So when/if the leg grows back, the light is blocked, the circuit is completed, and Somethingelse Lass gets fried by the electrodes.
A bit of a reach, but sillier things happen in both comic-book and pulp genres.