Its very easy to change them, but not to mix them. You need different pots. You have 25k pots with the EMGs and you'll need at least 250 (will work, thats all, normally a single coil pot), far more likely 500k for the BKs.
The MM is bassier, less middy similar teble, but its higher sounding, sharper, its lower gain, less compressed, more articualte and defined than an 81.