has anyone managed to link an invoice back to it's SO ? (Invoice's customer was changed by an end user & now reverted back)

Not sure what you mean by link back to it's SO but there should be a

createdfrom

field that links the SO to the invoice

What I think he means is that when you change the invoice the changes are not reflected on the so.

Once you break the link there is no going back. You have to close the sales order, delete/reverse the fulfillment and treat it as a stand-alone invoice.

Thanks michoel. Yea was hoping there was a tweak for it. cheers

I have seen instances where if you change the Customer On Invoice (using Script) before creation, then it will keep the link.