mr_fender
Axe-Master
However, if you turn a 500k pot down to around 7 or so, it becomes a 250k pot, so as long as you're careful and precise with the volume knob it can work, but it is one more thing you have to think about.
That's not how voltage dividers work. The resistance to ground is still 500K no matter how you have the pot set. You'd need another resistance in parallel to lower the load on the pickup.
Edit: Joe beat me to it.