I think I understand.25V buck boost transformer
doug - In all due respect, there is not one of us that has a clue what you are trying to do.
Limiting voltage to the GFCI logic circuitry could compromise the functioning of the GFCI also.The OP mentioned that the receptacles are GFCI. That is the best protection that one can use. The series resistance idea won't limit current to a safe range and will pose problems for connected equipment and devices.
The difference between getting killed by 110V and getting killed by 90V is lost on the victim's family...It's 110vac thanks . And what's with the negative comments from the others.
I'm trying to keep contact voltage down when testing there projects . Try thinking from A to Z.
I thought this site had class. Those of you that are bothered by question don't reply.
I ask for help , guess not everyone knows everything you gentleman know. So one more time. Students , voltage , safely.