No there is no way, that you can restart just your A-spec.
If you do want to race those events again, do it, because they are not blocked once you've done them ;D. But looks like that you want to get the cars/level tickets too that you've already have or did got.
I did consider backing up my save and then deleting it off the ps3, but decided a new account was a better idea. That way, I can still race online and be recognised.