Mine was changed last year with the bumper off. I would say its probably possible to do it without removing the bumper but it would be a kingsize pain in the jacksy.
bumper off, i did it with the bumper on and its a royal pain in the rear to do!
not much space bettween rad and bumper from underneith to move your hands
I managed to get mine off without removing the bumper, and i need it off again soon and im not looking forward to it. It is possible but its difficult What a cnut of a thing!