I'm replacing the pads on the rear disc brakes on my Ford Taurus station wagon.

One of the steps before installing new pads is to retract the piston by
turning it clockwise with a special tool, which I have.  I am finding it
nearly impossible to turn the piston, and I was wondering whether it might
be because I didn't remove the emergency brake cable  (the emergency brake
is released, but it seemed difficult to remove the end of the cable from the
lever at the back of the caliper, and I was able to remove the caliper
enough to replace the pads without removing the brake cable, so I didn't).

I'm just wondering if the presence of the emergency brake cable might
somehow be keeping the piston from rotating.  (I don't know exactly how the
emergency brake works, and the diagrams I've been able to find online don't
help).

Any suggestions?
Thanks,
Bob