It comes down to knowing how dark you want the tone, and how much you use the volume control.

If you typically run full volume then the taper has no effect, and even with a 500k in parallel it will just give a more linear taper when it is engaged. The overall darkening of the effective 250k pot will depend on the pickup and how dark you want it.

If you want a true ‘mud’ style switch with a push/pull you could just add either a .003uF or .012uF cap to ground, or even both with a trim pot between them so you can dial in the mud you want. Again, it depends on your ear.

For something like this where you don’t necessarily know what value components you want until you hear them and get your ‘sound’, it’s helpful to install the pickup but use clip leads to test different parts until you find what you want.

pickup - volume - output - clip on { pot (adjust amount of mud) - .003uF <-> .012uF caps - ground}