My guess is that is is a slender screwdriver that is adjusting some sort of internal trim pot on an active system? I thought Paul Wilczynski had a hand in that bass somewhere, but I don't see it on his website. I'm sure I've seen that bass before and it had a Yamaha Billy Sheehan/Attitude pickup up front, and was restored from a total wreck. Maybe I've just got a bunch of synapses up there making false connections.
All of those mods you've posted are not my thing, but well done to the guys that carried them out, purely for making a ballsy decision. No idea who thought two Dimarzio Model One pickups would enhance the tone of a Rickenbacker. Maybe they liked the feel of the Rick but wanted Gibson-style tone throughout? Is bass numbers 2 and 4 the same one, with a before and after shot? Same pickup setup (minus the neck in the latter) and Badass I bridge arrangement. Much better finish on the seafoam example, though I'm not sure what is going on with the pickguard.