I would've said no.
Don't think that the electrons disappear when the power is turned off.
They just don't "move" and doesn't generate electricity any more. (guess that is a bit simplified but I'm no expert 😉)
Besides, the mass of an electron is ridiculous small.
So any amount of additional electrons would just be this silly theoretically weight that you would not be able to measure.
/SK
As it's still attached to the wall? What is? And what are you saying no to?