So I've seen, BUT there are many threads that say that this isn't the case.
Does anyone have any experience of either method?
Assuming this is a GT, if it's one of the outer sensors they're easy to get at. Lie on the floor and reach up the back of the bumper and feel the sensor/spring and, with the other hand on the holder on the outside, push together and twist, it'll come apart like a bayonet (light bulb) fixing. Undo the electrical connector, which can be fiddly.
Your new sensor is unlikely to have the ring that the spring sits on, be very careful removing this from the old sensor.
The inner sensors are harder to get at, it's just about possible without completely removing the bumper. Undo all 3 bolts on the underside of the bumper, undo the single bolt behind the wheel arch liner. You may find this gives you enough play to get at the inner offside sensor, if not remove the 3 bolts in the boot behind the felt trim. That will definitely allow enough play to get at the inner offside. The inner nearside is a PITA to get at as it sits in a foam block, you will need to remove the bolts behind the trim to give enough play to get at that one, which if you have Bose will mean removing the sub.
Hope you have more luck than I did with the bolts inside the boot, the heads were rusted to hell, had to buy some mini cutting discs for a dremmel to take the heads off, wedged a hose pipe into the bumper to prevent heat deforming it. Have now replaced all bumper bolts with M6 hex bolts and penny washers, got black ones for the 4 visible bolts. Also had to buy a pack of new spire clips that hook onto the lip of the bumper that the inner bolts affix to.
Speaking of the visible bolts on the slam panel, one of mine was just turning, wouldn't come out. The rivnut it bolts into was slightly loose, if you remove the plastic trim inside the boot you can get a 9mm swan neck round spanner on the nut through the holes to hold it still while you undo the bolt. I've had the back bumper off a couple of times now, replacing the torx with M6 bolts makes things so much easier, give the heads and threads of the bolts a dab of grease when refitting. I even popped plastic caps on mine.