Open the loco for edit in CMP. Go into the Config file of #4449. Replace the kuid number in the hornsound tag to the one you want. Be sure to replace it in the kuid table at the bottom too. Save the config file and commit (Ctrl+M) in CMP. Check the dependencies by right clicking on the loco. Select view dependencies, and look to see if the hornsound is there. If it is, you can go and drive it.