Re: How to wire 250k to neck only on an HSS
If all you can do is the 2 pots, then yeah, a dual-concentric 500/250K will do it.
However, the only such pots I can find can only mount on pickguards, as the threaded collar is too short to go through a 1/8" solid top.
You can also use a push-pull pot with a resistor wired to the main volume pot that cuts it down to 250K. You might even be able to wire it to the 5-way so it happens automatically, but as was stated, it'd affect the neck+middle position.
You could also lower the pickup itself, put a solid cover on it (if the poles are flat) or simply replace it.
Or you could use an EQ pedal to cut the highs when you go to the neck.
By the way, would that be the PC1? The neck pickup doubles as the sustain driver, so anything you do to it will affect its operation.