If the cable is too long when you receive your seat post. You can shorten by doing the following:
Install seatpost with long cable, just don’t fully tighten the cable ties that hold the cable on the bike frame.
Determine length cable you need and mark on housing.
Remove thumb switch lid.
Loosen the two 4/40 cable set screws in the Switch Arm with the .050 allen wrench provided.
Remove cable from thumbswitch.
Cut a little of the cable end off so you have a nice clean un-smashed cable showing,
Pull the housing down over the end of the cable (so when cut cable housing to length, you don’t cut the cable inside.
Cut cable housing to length and push cable back thru.
Cut cable leaving just little over 1/2 inch sticking out of housing.
Push cable and housing into the switch with cable extending thru the switch arm.
Tighten 4/40 set screw, make sure no slack in cable, then fully tighten set screws.