No, the Model Select knob on the Variax 300/600 cannot be calibrated. If the model knob is "out of sync", try reflashing your instrument.
Variax Reflash, Software updates,and Troublshooting Tips
http://line6.com/community/docs/DOC-3857
If you are still having problems with the model select knob not selecting the correct model, you will need to have the unit serviced at your local Line 6 service center.
Product Repair
http://line6.com/community/docs/DOC-1606