Firstly the horn on the main mesh would have to be a node that is able to be toggled to turn it off and make it disappear entirely. But this is not the case. You're stuck with the model that is on there, adding a new horn child would make it so you have two horns.
Anthony Wood Audio Engineer - Searchlight Simulations
It's things like that and other effups that I wish RW was like MSTS where you could alpha channel parts you didn't want away and replace with your own child objects.
Anthony Wood Audio Engineer - Searchlight Simulations