I'm not sure what your modification has done, but you do need a capacitor for the pot to work as a tone control.
You could put in a lower-value cap so the tone control doesn't roll off the highs so much, but if the basic problem is that the guitar's too dark with the tone on 10, that won't really help.
If you want a tone control, but you also want the pickup to be generally brighter, you could try replacing the 500K volume pot with a 1Meg.