You can apply individual rates to a client. When you set a rate schedule, that rate schedule's will be suggested automatically when invoices are created. You can override this on a per-project basis in the project detail screen. The project's default rate schedule will then be suggested instead.
Setting a rate schedule for a project.
Navigate to the Client
Select Projects on the top toolbar
Select the project you would like to apply a rate schedule to
Scroll to the Billing Section.
Select a rate schedule from the drop-down in the rate schedule override
Click Save.
Setting rate schedule for specific projects from rate card
This rate schedule will override the rate schedule that you may have set up for the Client.
Navigate to Billing
Select Rate Schedules from the top tab bar
Choose the rate schedule that you want to apply to a Project
In the overview there is a project section, click on this for a drop-down menu of all the Projects.
Select the Project or Projects you want to use this rate schedule
Save