For years now I've been recommending the use of Paid Transaction Removal for AR to move paid items to history and improve both AR and Collections management performance. One of the problems with this approach is that it it's difficult to unapply a payment after Paid Transaction. Now that the Professional Services Tools Library is free, this gets to be a whole lot easier.
PSTL includes a Receivables Management Unapply tool designed to unapply payments from the history table and allow user to apply them to other transctions.
The tool is really easy to use, simply run the Receivables Management Unapply tool, enter the Customer, find the item to unapply and an uncheck the box. The system will ask if you really want to unapply or just see a report. Indicate that you want to unapply and that's it.
A report does print with specifics. There are a few caveats and specifics around discounts, writeoffs and Multi-currency so be sure to read the help file included with PSTL.