Yes, corrections can be made both before and after an employee has been paid. If the payroll has been processed, the submission has been sent, but the employee has not yet been paid, you can easily do this and the software will automatically make a correction to the submission.
Payroll software will also be able to handle corrections after the employee has been paid. You can create a correction submission, and when sent to Revenue, this will replace the original submission. It is worth noting, however, that frequent corrections to the payroll may result in Revenue intervention.