How difficult would it be to change the location of my bathroom fixtures?

If this is your typical 5 x 7-foot or 5 x 8-foot bathroom in a post-1970 home, moving fixture locations shouldn’t be terribly difficult for someone with more than basic knowledge. If you stay within that same footprint, you can keep the plumbing stack venting as it is. Once you get more than 5 feet from the main stack, additional venting will be needed. Homes built before the 1960s, however, have mud tile set on walls and floors, making things a bit more difficult to deal with. The other challenge is dealing with cast iron or copper drain and water supply lines. The end of the 1960s found us switching over to plastic drain/waste lines. These are easier to cut and move around.