I've never heard this before. I hope someone will chime in with an explanation.

I have heard never to prune/truncate a main climbing rose cane. If a cane is old or damaged, remove it at the plant's base. Obviously, deadheading is different and would be allowed.

Yes. I think one can cut laterals, but not the main can as lateral grow from it. It is supporting those laterals. By cutting it one pushes the growth lower creating more of a bush. However, one can train a lateral to take over the dominant position. Tips have something called apical dominance which explains why pulling a can horizontal pushes laterals.

so it is possible to develop/replace the main cane?

i have found other plants with apical dominance usually don't recover their natural height if you pinch out/or damage their growing tips (they just get bushier)

A new basal has to grow to replace a main cane, which should happen.

The main types of climbers are... Those that are bred as a climber, those that are bred as a floribunda type climber and those that have sported from a bush rose because there were strong climbers or had many climbers in the background. These types will sometimes revert to the original bush they sported from if you cut the main cane hard. The idea was very popular many years ago because if the bush had been a vigorous one, it easily reverted back.. Even to day, I would not prune the main cane hard. I would just wait until it had grown to the height I wanted and then in the spring cut it back so when it puts on new growth it will come back to the size you wanted. Floribundas always make the nicely shaped climber. Sort of like a pillar. The reverts can be gangly and when you prune them they get mad and get messy looking. Modern climbers are much more discipline.