Just a quick tip...If you cut the wires and later want to put a regular switch back in...
If the wire is a number 14 you can put both under the screw terminal if you cut the un-broken wire. Be sure if you cut the wire to mark the 2 ends so you don't get it mixed up with the other one.
If the wire is a number 12 wire then putting 2 of them under one screw terminal is a bit tougher but can be done and will tighten up.
When you make the small loop to go around the screw terminal be sure to put the open end of the loop in such a position that when you tighten the screw it will try to close the loop rather then open it. (when looking straight at the screw, the solid side of the wire is on the left and the open end is on the right.) Also it is a good idea to close the loop with a pair of needle nose pliers after its hooked around the screw. This will help it from squishing out when tightened.
Another note, if you cut the wire and put the 2 leads together with the wire from the X10 switch you will need to use a
red wire nut. The
red wire nut will handle 3 number 14 wires or 3 number 12 wires or any combination of the 2 wire sizes.
Could I just leave that wire unbroken and connect the black wire of the WS467 to it with electrical tape?
I wouldn't recommend this method. You can not get a good mechanical bond doing it this way. Also it is not recommended to solder the wires and tape them. In most locations soldering house wiring is not allowed. (To many people use the wrong solder type)