It will work. You can have the variable resistor (potentiometer) first in series and then capacitor to ground, or the capacitor and then the variable resistor to ground. It works exactly the same.

The capacitor runs between the signal and ground and passes all but the low frequencies. The potentiometer is wired as a variable resistor which limits the amount of current that flows down to ground via the capacitor, and the more resistance there is in that circuit, the less high-end gets passed to ground. With the pot fully up, you should have 500k ohms of resistance, so almost nothing at all flows, so you get maximum brightness from the pickups. With the pot fully down, there is no extra resistance, so all the high end signal flows to ground, leaving just the bass. Somewhere in the middle, you have some of the highs flowing to ground, but not all of them. So in this instance it doesn't matter if the variable resistor is before or after the capacitor, it does the same job in both locations.

In some circuits the sequence of components is important, but here it's not.