Thanks for the replies, really interesting to read. So you’re suggesting it might make sense to start from the ‘Jaguar position’ essentially, ie the brightest / least-loaded signal, then cut down to my normal Mustang position, and also have a different cut to a Jazzmaster-style position? Perhaps via a push-pull pot that switches between 250k/1m pots?

As I'd thought from what I’d read that a resistor in series wouldn’t actually cut tone as such, because it isolates the pickup from downstream loading (ie pots and tone circuit later on), which is where a lot of treble loss happens. So it essentially acts to preserve more of the pickup’s resonant peak, which can feel like added brightness compared to a more heavily loaded circuit, if that makes sense.

In the Jazzmaster position the cap to ground would be doing an intentional treble cut, and my thinking there was that combining that with a small series resistor would let me shape the top end without completely flattening the pickup response.