did mine when i rebuild my 20v after the tensioner pully failed....
not too hard, just more of an arse than anything, if i didnt have had to remove the head etc it would have been alot easier, the engine mount you have to remove is a tw@t, also the m5 threaded bar with nuts on (which you need to remove tension from the tensioner spring loaded pin) is a bit of an arse too. but if i had to id do it again as now i know what/how to do it its easier....
although i will say, if you let a garage change it (belt/tensioner) you have the beauty of some kind of fall back if it all goes tits up 10miles down the road...... if you d.i.y it and it goes tits up........
costly....
