I don’t have the answer, but here’s a thread on changing bass response. You could always take there advice and add in a high pass filter. However, I’ll see myself out and let the knowledgeable folks chime in https://www.diystompboxes.com/smfforum/index.php?topic=55058.0
I tried the bass switch Dino traced here from his reissue version. It's the one with a guitar/bass switch. I liked it better than the usual Rat bass Ruetz type mods as it didn't change the distortion character, it just allowed the lows through.
As someone directly involved with the thread srf86 linked to I can wholeheartedly recommend the bass pot mod. Really easy, and makes the pedal so much more useful to me. I love it!