How to adjust operator settings after leaving the settings panel I've added a torus knot using the the "Add Curve: Extra Objects" addon. I've done some work on the scene, and now would like to go back change the knot parameters that were in the operator settings when I first added the curve. 

How do I get back to that panel to adjust operator settings?
Unfortunately, you can't. Once you perform another operation, the changes are set.

However, the operator should retain its last-used settings; you can delete the knot and re-add it, then change the settings to suit your liking.

If you want to change the settings before doing anything else, you can use the panel in the Tool Shelf, or press F6 in the 3D View to bring up the options for the last-used operator.