Not straight forward way, but not impossible either. There may be a better way, or a short-cut within the following procedure, but I would play it safe.
- backup locally to JEX (this is your complete backup to avoid nightmares)
- delete the password (or all passwords) under prefs > master keys and click save
- Jolin will show a red cross behind the password entry
- backup locally to JEX (this is a 2nd backup without passwords)
- log into your cloud/sync space with your browser (not Joplin) and delete everything
- delete everything from other devices (other then your primary desktop device)
- delete your local profile folder completely (or move it)
- reinstall Joplin (clean slate) and create just one note, encrypt it with a new masterkey and password, and sync it
- re-import your other notes from the second backup
- do not enter the old passwords when prompted
- select re-encryption and patiently wait for this to end
- this should apply the new masterkey to all your notes, and the new masterkey is protected with the new password of your choice
- sync with your cloud
Check this "draft" procedure carefully, and see you understand the concept.
No promises, as it's written off the top of my head, but it worked for me about 6 months ago.If sth goes wrong, think before panicking. Start recovery from the second backup, to which I assume you still know the password. If all fails, start with everything fresh. You do still have the full (first backup). Nothing is lost unless you mess it up. It is fail-safe if you stay cool, it is not otherwise.
Let me know if you were up for it, and if you succeeded. And if you shied away from it all, let me know too. I know you were looking for an easier solution. But you won't do this every months - right ?