RE "However, if they will be moving back to MD and will still work in CA"
The OP didn't say the employee was moving.
In any case I don't really understand. How do these steps help the OP change the employee address?
Also, the OP is clear that the employee "work and reside in CA". How then would they be subject to employment taxes in another state? I don't think that's allowed by law. Is there something I don't understand?