Thanks for the price update.
I did have the official procedure but cannot find it at the moment.
Anyway its,
Wheel off
Remove Wheel arch liner
Drill out the two rivet holding metal box over alarm unit
Remove box with siren,
Unplug siren.
Lift siren out of metal box.
Then refit is reverse, but you need two new rivets.
Not hard, you would think even a VW tech could do it
The first one mine needed was still under warranty, the dealer refitted the wheel arch liner back on with I'm guessing an electric screwdriver and the screws so tight they cut right through the soft wheel arch liner plastic, result when i checked, new liner needed and another trip to the dealers...