Yes on a 2 conductor pup you can't coil tap either.You can however add a out of phase switch still,in the middle position on the selector switch you'll get a straty tone.
As far as having a 4conductor cable added it won't effect the pups sound at all.BC Rich used to use guild pups in the seventys,they were all 2 wire and they opened each up and added the 4wire cable on.Just peel the tape of very gentaly and don't chip off any more potting wax than needed to add the two extra wire,retape it and glue the end were the tape over lapes you should be fine.