LAPS Intune policies

SebCerazy​ 

for the LAPS CSP and the PasswordComplexity you do have a "Delete,Replace" under the description Framwork properties, see the link bellow:

https://learn.microsoft.com/en-us/windows/client-management/mdm/laps-csp?WT.mc_id=Portal-fx#:~:text=configured%20to%204.-,Description%20framework%20properties%3A,Expand%20table,-Property%20name

So, I would create a new group for those with the old passwords, exclude them from your current policy, and if everything goes well, redeploy them later with the new LAPS passphrase policy. 

Try it first on a test machine or only 1,2 devices.

Good luck!