Thanks so much to the OP and contributors to this thread, I finally managed to complete this DIY this weekend. My belt had been squeaking a little at idle after cold start for the last 10K miles or so. I figured that since I had just passed 100k miles, I should replace the belt, tensioner and pulleys (the horror stories of the belt getting sucked into the engine block terrified me).
I don't know why, there are plenty of youtube videos on changing the N52 belt but none on the N54... Actually, I know why - it's so much harder with that annoying air duct going from the air box to the turbo.
Unfortunately I also broke the coolant vent hose when unclipping it from the fan, and then the upper radiator hose nipple that connects to the vent hose. Getting that repaired cost more than the 2 hours of labor that the local indy shop quoted me for doing the belt and pulleys. Sigh.
In the end though, I found it very helpful to remove the radiator fan. I'm not sure this job could be done without removing it. The rubber grommet that attaches to clip on the air duct coming off the intercooler was a real pain. Every video I could find involved first draining the radiator and removing the intercooler, which I didn't want to do.
I look forward to not having to do this again for another 100k.
