To modify the amount paid to a salaried employee in a specific pay period, follow the steps below:

1) Create calculations as normal without paying
2) Go to records > Employees and  open the Employee record
3) On the Activity tab, open the unpaid calculation
4) On the Calculation Summary tab, click New Pay Type
5) Select the Pay Type ID the employee typically uses
6) Enter the effective dates
7) Choose Fixed amount from the Rate drop down
8) Select Amount per period from the amount drop down
9) Enter the total gross amount to be paid for this period
10) Save and Close the New Pay Type
11) On the Calculation Summary tab, highlight the original Salary pay type and click Delete from the dark grey menu
12) Save and Close Calculation
13) Pay as normal

Note: This will only modify the calculation. Next pay period will calculate the scheduled salary amount that is defined on the employee Compensation/Deductions tab.