Hi Ulrich, welcome to the Club!
It should be fairly easy to switch the P and J connections on the pan pot. There should be two brown connectors attached to the pan pot- carefully remove them (there's a lip thingy keeping the plug down) and plug them in again in the correct order. Not much room for manoeuvering in there, so you may be better off taking it all out of the instrument. You might want to wait a little because...
The pickup balance issue is well known, and there's a
Pan Preamp available from the webstore that actually adds a second preamp, so you can set the gain for each pickup independently. Though on a pan pot, I don't think you can completely silence one pickup.
I would also recommend shielding the electronics cavity all around, to where the brass backplate touches the wood, and where the pots and jack pass through the wood. You might then be able to take out the earth wires.
