Transmogrify CoSequentialIdentifierAssignments to FormatAssignerSequences. This is complicated because all Identifier Assignment is now plugin based, so either TransmogrifyCommand needs to instantiate the plugin, or Transmogrification needs to be manually rerun (just for this model) to migrate the sequence data after the plugin is instantiated by the administrator.

Additionally, permitted_characters should always be populated (it might be NULL in some legacy circumstances).