Yes, then it make sense to try to cover this logic in before provisioning rule. Ideally, i believe you should then cover account move, email regeneration and proxy addresses in before provisioning rule as that would be the ideal scenario.
The after modify rule is also another approach but then you will need to write the powershell script and still might need some attributes to be included into the provisioning plan to perform the checks in ps script.
So, it will be better to align with Expert services, as they can suggest other approach as well by looking into your system and use case.
Please let me know if there are any queries.
Thank You.
Regards
Vikas.