Hi TonyTan,
While we recommend using an ad hoc pay run to record changes made from previous pay runs, you can certainly unlock and edit an existing pay run if you choose. If the pay run is the most recent, you can also re-lodge it. However, we do not recommend lodging events out of chronological order and if the pay run fell some time in the past we would suggest lodging an Update Event instead to ensure the data held with the ATO is correct.
-Kass
