You will be able to "swap" old style stamps starting from March 2022, but as I understand it, this will need to be done through the post accompanied by a special form, not at post offices. The Royal Mail's relevant website page isn't up and running yet, so watch this space.
So all those of us who have bought stamps in bulk before the annual prices increases, and still have them hanging around .....
A couple of news items:
The sensible one - Salisbury Journal
https://www.salisburyjournal.co.uk/news ... uary-2023/
The hysterical one - Daily Express

https://www.express.co.uk/news/uk/15640 ... s-reaction