To automate this you will need a custom script that can call Update Entitlement in Bulk API. The API does have a limit of max 50 entitlements to be updated at once.
If you wish to do this via Postman, you can design a Postman Flow to do it.
The question and suggested solutions seem not exactly lined up. You ask about possibilities during the aggregation. None of suggestions however are part of the aggregation flow. If you really mean aggregation, then would not just group aggregation rule fit?
In IDN there are no group aggregation rules available to update entitlements during aggregation, so you need to update it beforehand , so either your 3 options or you can follow the suggestion Sharvari has provided.