Porcelain is a strong material, but once veneers are cemented, only very small adjustments can usually be made with polishing or slight reshaping by a dentist. Making them significantly shorter or less wide might risk damaging the veneer or affecting how it looks and functions. Sometimes, if the change is more than just a minor tweak, replacement might be the better option. It’s definitely worth bringing up with your dentist so they can evaluate what’s possible without compromising your smile.