I used a hair drier to remove some of the wax potting when I took the cover off my neck mule
also did it to my riff raff, although I put the cover back for the weird coolness (I love unmatched looks)
the difference isn't huge, but I can tell the mule now sounds more open and airy (it already was, anyway), but I removed cover AND a lot of wax (not only from the top and sides, but from the coils as well)
I have a friend that used to do that with his gibson 500t pups
the difference is definitely audible
both riff raff and mule are amazing rock pickups
they are both bright and open sounding, but the riff raff is edgier and middier, while the mule is warmer and juicier, but still retains some of the glassy top
hard to make a decision indeed, but it's a win/win situation