Nigel Burbidge
There are several ways of skinning this particular problem. Ones that probably won’t appeal, because you have already installed motors, include using the SEEP motors with built in micro switches (although, in practice, I found they are only marginally more reliable than the switches on the aged HM3 motors).
However, there is a tang coming out of the bottom of the motor, the other end of which is the point actuator. You can use that to push a metal bar or plate fixed to a separate micro switch to change the point polarity.
Nigel