My question is: How do these interact?

Say I use Riku to exhaust a Necronomicon curse or Curse of the Bell. It will refuse to exhaust (because it's necronomicurse, and this curse can never be removed...), still produce a new curse.

Apparently this new curse can be a Necronomicurse. If I pick it, do I now get 2 necronomicon curses in my deck?

And then the next question is: Do we get the 6 HP from Darkstone Peirapt, because we technically did just add a curse to our deck permanently?

And then finally: What if we are facing a weak enemy, could this be used to gain tons of HP? I suppose you would want DuVu doll as well before it makes sense, still...

It might be rare enough to be another novelty combo I suppose. Food for thought. I might try to setup a custom run with the curse set and a No Game No Life start to find out what happens. Perhaps it might also be easier to bootstrap than I thought earlier: just by having a curse or two you can fish for necronomicurse(s).