The main reason is to use portal type setters, and not set the properties
directly: setting the properties directly bypasses interactions which
trigger type refresh, which hence prevents such changes from being applied
to the types until something else would cause a reload.
While at it:
- modify the property sheet list once only instead of once per added
  property sheet
- only modify the property sheet list when fixit is true
- improve constraint message to actually tell what is being detected
- do not report a constraint error when no change is necessary
- follow naming conventions: avoid abbreviations, variables holding
  documents must end in "_value"
- avoid single-use local variables