Watching Seabiscuit where Rosemont came from behind. Wondered if now Jockeys can be wearing an earphone and have a spotter warn them about horses coming from behind?
I can’t answer your specific question because I don’t know if it is allowed or not - but the difference between an average jockey and a good jockey is the ability to “read a race” and to have a good deal of spatial awareness. In the rush of a race, where opportunities or problems arise in a split second, having someone instruct the jockey about what is happening is unlikely to be helpful. It would be a distraction.
By the time the instructor verbalized the instructions, and the jockey attempted to enact them, 10 things might have changed in the race.