When performing mass updates on positions or employees, you can overwrite or fill data as follows:
Overwrite:
Existing data and assignments are updated with new defaults. New assignment rows are not created, but existing rows are updated.
If salary or compensation details do not exist, the new defaults are not applied.
Fill:
Assignment rows for the new default data are added to position and employee details.
If salary or compensation assignments do not exist, new assignment rows are added to employee and position details.
See Sample Mass Update.