ability to mark invoices as paid even when they are no longer linked to quick books

We no longer use Quickbooks integration but the invoices raised when it was linked to our BM means I cant edit the invoices or mark them as paid (unless paid in full), also i cant add a part payment on these invoices either as they were done in BM when we were linked to QB, makes no sense really so I have to wait for the invoice to be fully paid before I can mark it paid so i cant send the statements from BM as they are incorrect