It's easy to change the bedding; not quite as easy to change the stickers (unless they peel off easily). Could you not decorate the room simply and then personalise it using soft furnishings and so on (things which are easy to change as he grows up)?
Thanks for your reply... I checked the stickers and they do peel off easily. I also asked my 9yo son to have a look and he thinks it'll be ok for a couple of years so I think we may just go for it. We've been renting till now and DS2 has had a tiny, barely decorated room so I really want to make this one special for him!
I think they look great. I can't say if he's likely to grow out of them quickly, not much experience with that age (yet). I don't think my 9yo nephew would like them, but if they are easily peelable then you can just change them.