To exchange one kuid for another, go into the locomotive config.txt and scroll down until you come to the hornsound and change the kuid number from the built in one to the one you want to use.
There may also be a kuid list at the bottom of the config.txt ( maybe not for the older locomotives on the DLS ) but if there is one there, you need to alter the hornsound kuid number in there also. Click to save and exit and you should be good to go.
Cheerz. ex-railwayman.