How can I change / add a balance vacation days (if the HRM module is activated)?
You can add a balance by clicking on the 'pencil' in the 'Available as of today' field, see below:
This is also the way to add (overtime) hours to a time-back (TVT) leave policy.
If you do so, you have to enter the number of hours, the date and a description / explanation, see below. After that these hours will be added to available hours on the date entered and the description will be visible in de the green 'Accrual details' overview.