right assuming you dont have BPCore, the way to do this is as follows.
Right i will be using a SFX for this called Gen_red_alert.wav. you can call your SFX file whatever you like. and i will be modifying the nebula bridges script
firstly go to the root bc directory and place your SFX file into the SFX folder.
Next go to Scripts/Bridges/ and open up nebulabridge.py using notepad
Scroll down until you see the def LoadSounds() and type the following code as shown below.
def LoadSounds():
# debug("Loading nebula red alert sound")
pGame = App.Game_GetCurrentGame()
pGame.LoadSoundInGroup("sfx/Gen-red_alert.wav", "RedAlertSound", "BridgeGeneric")
make sure you also set it to def UnLoadSounds()
ldef UnloadSounds():
App.g_kSoundManager.DeleteSound("RedAlertSound")
There are a few different types of sound that i discovered could be changed.
they are
LiftDoor
GreenAlertSound
YellowAlertSound
RedAlertSound
Hail
To change these sounds copy this line of code replacing the SFX file and the highlighted to one of the ones i have written above. Also dont forget to unload the sound
pGame = App.Game_GetCurrentGame()
pGame.LoadSoundInGroup("sfx/Gen-red_alert.wav", "RedAlertSound", "BridgeGeneric")
if your still unsure try having a look at
http://bridgecommander.filefront.com/file/Unique_Red_Alert_Sounds;26110i reccommend
NOT installing this as it is now dated for many bridges.
Also make sure you always make a back up before modifying any script.