Plugin to cleanup/remove unused user defined keywords(IMAP PERMANENTFLAGS) possible ?

I found a reference to a similar issues here: https://www.dovecot.org/list/dovecot/2010-March/047925.html

I know IMAP rfc say nothing about removing the keywords/PERMANENTFLAGS (they can only be added https://www.rfc-editor.org/rfc/rfc3501.html#page-64) , therefore I wonder if it is possible to create a Dovecot plugin to accomplish this task ?

Technically it is possible to do now via the following steps:

1. Ensure the "unwanted" user defined keyword/flag is remove from all messages in a folder (Folder A)
2. Create a temporary folder (Folder A_temp)
3. Move all messages from Folder A -> Folder A_temp
4. Delete Folder A
5. Rename Folder A_temp -> Folder A As you can see this highly inefficient and awkward and even if the unwanted keyword does NOT appear in Folder A anymore , it still can be found in '~/Maildir/dovecot-keywords' file

Alternatively, if it is hard to create a plugin that would remove the keyword for good, would something like this be easier:

1. Define a list of "allowed" user defined keywords 1a. Perhaps this list can be defined via METADATA extension on per folder basis
2. Reject(or discard) "not allowed" keyword sent via the +FLAGS / +FLAGS.SILENT commands

Any helpful plugin example or code references would be greatly appreciated.

Thank you very much,

Sergey Mosin