Will a bonnet trim on my car that I can't clip back in fully on one edge due to being shunted by someone and it getting bent be an mot fail?
It could be if it's likely to pose a possible danger to pedestrians. Impossible to say without seeing it, really.
If you're worried best thing would be to put some tape over it, preferably something like Duck Tape.
If it gets removed by unclippping it would that be okay?
If any sharp clips are left behind they could also be an issue.
I thought that too. Any chance the OP could put a picture on a photo sharing site and post a link?
Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.