No its not difficult at all its held on by the screws that the parcel shelf string attaches to then there are 2 poppers about a third of the way in on each side. Just off the top of my head there may be another couple of screws but that will be apparent if you have a look around it. Then you need too flex it a bit from the bottom either side to get it out. I dont think that you have to take off the grey bit to get it off sorry i have only done it once in the summer. If you do need to take off the grey bit it is another 4ish screws and more poppers.
When you take the surround off the poppers be carefull as one of mine snapped but that was only because i didnt know where they were.
Most of the screws will be star and pozi type.
The actual break light is held on by another 2 screws star type then it is easy to disconnect similar to speakers.