Make up-front payment work when adding guest after initial reservation

Currently, editing a reservation does not require upfront payment, even if the cost is inflated.

My club charges for guests, and we require up-front payment. This mostly works well, but members often add a guest to a reservation after it is initially made. In this case, up front payment is not required, and  they often just skip payment. This requires manual work to find those cases and obtain payment.

If up-front payment is on, it would be great to require it in any case where an existing reservation's costs is inflated.