Return order Quantity / Item Validation

Dear All,

I have 2 business requirements:

1)Return order allows to enter any material irrespective of materials mentioned in invoice.

My requirement is system should only allow to create return order for materials mentioned in Invoice.

2) If I enter quantity more than invoice quantity in Return SO, first time system gives error message. But let say i create partial delivery & then again if I return any quantity system will not stop. Example: In invoice i have 100 pieces, i tried to create return order of 120 pcs, then system will give me error message. Now i created partial return SO of 100 pcs and saved it. Now i created a new return SO of 80 more pcs, system will not stop me(it only gives warning message). My requirement is to stop it.

Regards

Rahul