As soon as an employee is paid for the first time, the 'Old Payroll System' figures become disabled. This happens because PAYE is calculated on a cumulative basis. These figures are used to calculate the first and subsequent payments. Changing these figures after a payment has been made, would make the payment incorrect.
Older versions of Payback does not allow any of these figures to be altered, but the most up to date version allows the Employer PRSI, Employee PRSI and insurable weeks fields to be changed. (These are calculated differently)
Most up to date version can be downloaded here;
http://www.payback.ie/support.shtmlIf you need to change any of the other figures, you will have to rewind all processed payments for the employee first. You can do this more quickly in the 'Year View' screen. Note that when you reprocess the payments, the results will probably be different.