EMG circuits like in the DG harness go with 25k and 100k pots. If memory serves me, the Clapton mid boost has a 50k volume coming after a first transistor. The Jackson mid boost circuit in my old trusty CH4 has that too, after the whole boost chip involving an op-amp instead of multiple transistors...
To go back and forth between active and passive electronics, it shouldn't be that hard to change a 250k in a 50k thx to a switchable 62k resistor in parallel (or to do the same with a 500k + a switchable 56k). The only problem is to know where the volume pot is located in order to decide how to implement such a switch.