A monthly payroll has 12 periods, but a customer requested a 13th run, so that all corrections made over 2010 would still be processed in 2010.
By using the standard processes a little bit smarter, we achieved the goal.
Retropay was launched so that the differences were created in December again.
The Payroll ran again for December with an element set, that contained only retro element types. So only the differences found by Retropay were processed by the second December run.
And just a tweak of the (custom) payslip, so that only run results of that latest run were shown, completed the picture.
And the post-payroll processes pick up all results of both December runs.