Can a gravity flush toilet be swapped out for a pressure-assisted toilet? Are there any differences in plumbing, mounting, etc.?
It looks like there's no difference in plumbing requirements from this installation guide.
This regular toilet installation guide lists the drain and vent requirements:
As far as retrofitting a pressure assist vessel into an old gravity flush toilet, I wouldn't try it. Pressure assist toilets are designed differently than gravity flush ones. Flushmate's website warns:
There might be a retrofit kit out there somewhere, but I'd be wary about how well it would work.
Yes it can. There are no differences on the outside.
There are even some pressure-assist valves that can be retrofitted into existing toilet tanks.