Re: GT parking sensors / bumper removal
Yes, I have done this for exactly the same reason and it is a DIY job.
First undo the bolts you can see on the top lip of the bumper under the boot shut (star thread - not sure what they are called).
You then need to remove the boot carpet and then carefully the side trim carpet that lines the side of the boot. Then, you will be able to access the series of similar bolts that bolt down through the bodywork and into the bumper.
Then (or maybe better before), jack the car up and remove the rear wheels and pop the car on axle stands. This will let you get at the small screws that hold on the carpet like guard in the rear wheel arches. Once these are loose or removed, you will be able to access the last of the bolts that hold on the bumper.
I did all of this on one side and then swung down the bumper enough to be able to access the reversing sensor.
I then cut a new notch in the outer plastic sleeve and then reconnected the sensor before putting the bumper back on again. This took me a couple of hours as I had nothing to go on, but again, it could be done in under 30 mins if I got a move on. Think I have remembered everything!