I think he should be fine if he's happy enough to flick water in your face! That made me laugh, my rabbit used to smile at me, and it wasnt aggressive either! Wish I had pics! Keep an eye out for any laboured breathing, excessive (more than once in a short space of time) sneezing and looking generally unwell. If you do want to move him on to another brand of food, you should do it in stages, I.e. 90% of his old food, 10% of his new, then a couple of days later 80/20, then, 70/30, you get the picture.
I'd say maybe take him to the vets just in case there is an underlying problem like pneumonia etc but he sounds like he's just fine :)
Good luck! :)