Depending on your configuration the Project Manager can change the default hour rates and set project specific hour rates for the resources in his project.
Set project specific hour rates
Step 1. Navigate to your project, to the tab Resource Management, sub-tab Resource Rates, and click 
.
Set project specific hour rates
Step 2. In the section Project Resources, enter the project specific hour rates, and click Save.
Note: Project specific hour rates can only be set for users with a project role.
Note: Project specific hour rates are active from the moment of saving and have no effect on costs of hours in the past.