A month ago, I whined about the floor register being right in the middle of the floor. I pondered getting an HVAC contractor to reposition it, but I first explored the possibility of doing it myself and it turned out to be a relatively easy job. I wanted to move it directly to the right, towards the toilet, and--what good fortune!--the duct ran right under the line along which I'd be moving it, which also happened to be parallel with the floor joists. So I had only to remove the 90-degree elbow that lead straight up to the register, cut off about four feet of the duct, then reattach the elbow piece and (after giving it a 90-degree rotation so it'd line up with the hole I had cut between the wall and where the toilet will be) the piece leading to the register. After using some duct tape on an actual duct for the first time in my life, I was done:
It was one of the rare jobs where everything just seemed to work out.