Yes, it's a tank off job. While you might conceivably be able to do it with the tank in place it would be a right royal pain in the arse.
To get the cover off you need to remove a few screws but there is also a mounting *Thingy* that the breather BOS is bolted to. You have to remove the ECU and then the *Thingy* before you can get the cover off. Then you loosen the alternator mounting bolts and release the tensioner bolt to allow the alt to drop down far enough to get the new belt on.
It's not difficult, just fiddly.