How to implement new PTO accrual logic in the middle of the Year without affecting the previous valu

Hi All,

Could you please advise me on below situation,

I have modified a PTO formula in update mode from 06-JAN-2020 with a new accrual rules. But I want the employees accrual as on  05-JAN- 2020 to be unchanged and continued to next periods.

First Pay period for 2020 starts from 23-DEC-2019 to 05-JAN- 2020 (Employee accrue 2 hours here, as per existing PTO Rules)

Second period starts on 06-JAN-2020 to 19-JAN-2020 (Employee will not accrue any PTO as per new PTO Rule )

After my changes applied on 06-JAN, when the accrual calculates for 19-JAN-2020, first periods accrual is also recalculated as 0. But I employee shouls have 2 hours on the period 1 and from period 2 employee should accrue 0 hours.