Susan:
Allow me to interpret your response and to play devil's advocate. I think your concern is that, without validation of the Report Group, a user could type an incorrect value into that field.

So to avoid that risk, you are jumping through hoops with the Account Set code, making your life difficult and bumping up against a (current) restriction of AP.

Why not use the Report Group as it currently exists? I agree that validation is very useful but it's not absolutely necessary. You rely on your staff to enter a Vendor's name and address correctly and, more importantly, to enter dozens of AP invoices correctly every day. Why not rely on them to assign the correct Report Group code?

I wouldn't expect that Vendors are added in the dozens nor that they change Report Groups that often. You can police the Report Groups simply by creating a GridView report that scans the Vendor list and looks for incorrect codes.

It could be that I am over-simplifying your situation and you will point out that there is something I am missing. Your thoughts?