Mercury? Isn’t it opaque and fully reflective? Or does UV light pass through it?
For initial testing, the FEP would remain, but as this liquid would theoretically not stick to the resin, the FEP would remain intact, pretty much eliminating risks that have anything to do with it.
I have seen something like this before, but it uses two different lightwaves in order to make the denser liquid remain inert, so it’s impossible to try it with consumer printers.