The printer surgery was a success. Here are a few notes for anyone else going this route.
In general, the instructions that came with the new belt were clear. Do be sure to open the lid while the power's connected so the printer cartridges slide into the middle of the axle. Then unplug the printer and begin surgery.
I got confused removing the printer's end caps. The instructions say "there is a plastic tab on the front and back sides of the printer." If you turn the printer over, you will see two tabs. These are not the tabs you're looking for. Instead, you want tabs along the front and back edges:
Here's a close-up of the clip. The bottom part is slanted. A piece of metal fits between it and the top one.
That means you'll be putting your screwdriver into the little slot between the metal and the plastic when you're levering the plastic away.
Also, there's a sort of printer cess-pit on the right side. I think that's where the cartridges relieve themselves during cleaning.
Do not (as I did) accidentally drop the spring into the cess pit or you'll have a cleaning job on your hands. Um, all over your hands, actually.
In any case, surgery was a success. The new belt seems to be working happily.