Changing Engine Specs, Hornsounds or Inside Cab Views
Edit the CONFIG.TXT of the loco, this can be done with a text editor (notepad) in the loco folder (for TRS2004) or using CMP to edit the loco files (TRS2006/TS2009/TS2010).
The section you are interest in is shown below
enginespec {KUID:177548:68003}
enginesound {KUID:177548:68001}
hornsound {KUID:177548:68014}
interior {KUID:177548:55920}
They are always grouped together. Select the item and change the KUID:177548:nnnn to the one you have found more suitable KUID:xxxx:yyyy.
Save the file, and in TRS2006, TC3, TS2009/TS2010 commit the changes.
The loco will now run with the changes when you next start Trainz.