Hi!

Train sets sold by Märklin normally have a built-in slider switch-over: the pushing loco is fed from the slider in the control car.
This requires power conducting couplers and a switch-over module.

That's right.
Either modify the train or the signal setup - or the mode of operation (stop the train manually or with PC control at the right spot).

I just had the idea that a circuit track near the signal could turn the track power off for a long stretch before the signal. This would allow push/pull operation with unmodified trains. That would work automatically.

Or a manual solution: Take a two position switch, mark it "pulled train" and "pushed train" and wire it such that "pushed train" extends the unpowered section in front of the red signal. All pushed trains must have a similar length.

My suggestion would be to have instead of one signal with a switchable zone and an isolation track, to install two signals with a switchable dead zone between the two. This way, a train entered the signal zone from either side would stop within the zone if both signals were red. The dead zone would have to be long enough for the entire train to be in the zone. The locomotive would keep pushing as long as the signal in the other direction remained green. When both were red, power would be cut off.

I wonder why they could not integrate some kind of feature into decoders that would detect a red signal ping and stop the train and then restart the motor when the signal pinged to green?

Regards

Mike C