If your organization has made the decision to migrate your United Kingdom payroll processing to another payroll vendor, you should not change the employee payroll ID numbers. It is highly recommended you continue using the same IDs the existing payroll vendor is using. Changing the IDs will create a second employee record per employee with HMRC (the U.K. Revenue) and will lead to many pay-as-you-earn (PAYE) under/overpayment issues.
The website below confirms the need to report employee payroll ID number changes in the Real Time Information Full Payment Submission. Refer to the Employee Information section
at the below website: