I don't think either of the approaches - using the PageBuilder or creating/updating a Form - answer the question asked. Is there any way to edit and add fields to an already existing block, e.g. if I add a Nickname field to a Profile (i.e. adding a new text field to the Create and Edit Profile forms), how do I get the Profile Info block to display this new Nickname field? My instinct tells me this would need code changes.