Adding constraint to existing drupal commerce order item type field

I want to add a constraint to an already existing order item type field but the field settings say “There is data for this field in the database. The field settings can no longer be changed.”.

Currently the max. field length is 255 chars. I want to limit it to 100 chars and issue an error in the form if that number is exceeded. I would be happy if I could just control what’s submitted through the form without necessarily changing anything in the database.

Is there a way to do this?