RMA disposition of sub assembly as part of single release

We have a sales order that went out that includes an assembly with a single release line. Within that assembly, we need to receive a sub-assembly back with the RMA process and return to it to stock. The rest of the assembly is fine.

It looks like RMA processing only allows you to return the complete release/main assembly, and I was wondering if anyone had some tips on parsing out only the sub assembly we need?

If we do not put the sales order information in the RMA entry initially, and enter only the sub assembly part number, is there a way to link a credit back to that order down the road?

Thanks