seat removal

Is it rusty at all? Here's what I would try.

I'd spray a ton of PB blaster all over it.

I'd put another nut right on the end of the stud and bang it with a hammer to break up any rust in the nut. Not too hard because you don't want to damage the threads.

Then I'd clamp come vice grips down on the stud and see if I could turn the nut. Just be careful because you don't want the vice grips to damage the threads either.

You could also try an impact gun. It could possibly turn the nut loose faster than the stud will spin.

I don't think you can just put a wrench on the other side of the stud in the interior but I could be wrong.