Is there a way to update a supplier (backend?) for an active contract on a Purchase Requisition?

We currently have constraints around regenerating a new contract number from our contract management (not Oracle) system. We have come across situations where the contracts have the parent supplier but the invoice needs to be paid to a child/subsidiary supplier. Given that we haven't set up parent-child relationships and supplier sites, this is currently a challenge because we can only create PR for the supplier attached to the contract and we can only pay the invoice associated with the same supplier on the PR.

The proposed workaround is to create a new contract or regenerate a new contract number but this is also posing challenges even as an interim process.