Doesn't make sense. I use several BL pickups with modeling software and don't have harshness problems. A 500XL with 250k pots should be pretty sweet, even a little dull compared to 500k pots. I wouldn't add more resistance. The other two lower inductance pickups might have peaks in a harsh range depending on the cable capacitance. You should find out the capacitance of your guitar cable. My ~8' BL-150 cable is ideal with my L200SM, making it open and bell-like.

BL Equipped Guitars:
-Parker NiteFly V1 Strat type: Wilde L280SN/L200SM/L200SL/L280SL w/L-filter & MT.
-Agile ST-625EB: Wilde Microcoil S set.
gckellochguitartech