Yes, there are many CAD/CAM workflows where you can replace the referenced model instead of creating a new one, but this requires the software used for the process. If the new STEP file is oriented the same and the design has only minor changes, use your software's Replace Model or Re-link option. Your setups, work coordinate system, and some of the toolpaths can be kept, with the exception that you will need to regenerate and carefully check all setups, work coordinate system, and toolpaths before machining. When no direct replacement is available, you will typically import the new model into the existing project, and try to use any setups as much as possible. If your fixturing and machining strategy is set, you might only need to change the operations impacted by the changed geometry, rather than the entire job. What type of CAD/CAM software do you use (Fusion 360, Mastercam, SolidCAM, etc.)? The details of the process vary with the platform.
