The Ashkenazic custom is to wash and say hamotzi on matza all year round. The Sephardi custom is to make mezonot when it's not Pesach.
Is someone allowed to follow the opposite minhag?
I have heard precedent for sometimes washing and sometimes saying mezonot. For example, pizza. I wash if i'm kove'ah seudah, but not if i'm having it as a snack. The same with certain "breadsticks" and biscuits.
So now, the question can be interpreted as: Can an Ashkenazi decide that he is just having matza as a snack, and not wash; and can a Sfardi decide to be kove'ah seudah on matza?