Assign existing footprint to existing component in Circuit Maker?
You can have multiple footprints for each component.

http://documentation.circuitstudio.com/display/CSTU/Component+Management+in+CircuitStudio

Under the component, In the models tab, click add, then browse the pcb library for the footprint. You can delete the old footprint or I believe there is some way to select it. You can also do this for one component only if done through the PCB editor and not the library