Hi @Pio Egan , if I understand your question correctly there are a few ways you can do this. The first is PowerShell. This will remove the users based on your query. You can also do this manually in the portal.
Based on how you add users, you could check if the user-id already exists, and then delete the old one if so (using custom policies and PowerShell). If needed you can check for other user attributes as well.
If I misunderstood your question please let me know and I can help you further. If this answer helped you please mark it as "Verified" so other users may reference it.
Thank you,
James