How can I still register Cost centers in historical pay runs that are closed?
If you have processed pay runs in the past without Cost centers connected to employees, you can enter the Cost centers now and connect them to the employees. Please make sure all employees are always 100% connected to one or more Cost centers. If not, the salary journal will not be complete.
After that, in Reports/X4 Salary journal you can now Group by Cost Centers, select the Cost centers (see below) and generate salary journals based on that selection, also for pay runs processed in the past. So you do not have to reopen these closed pay runs to have them registered in Costs centers.