By default, the tab is populated from the employment contract and its previous changes. To indicate new changes in the employment contract, you can mark some vacation types as not applicable to the employment contract and add new vacation types. 
The "Employment Contract Change (create)" form. The Vacations tab
To indicate that a specific vacation type is not applicable to the employment contract anymore, clear the A(Active) check box. Then, starting the effective date, the vacations of the type will not be available for the employee.
If you need to add new vacation types to this employment contract, click Add to add a new line. In the Vacation Type column, select the type of vacation applicable to the changed employment contract. Specify the duration of vacation in the Days per Year column.
A check box in the Main Vacation column, indicates the main vacation type for the employee. There can be only one main vacation type and multiple other vacation types for each employee.