Heh yeah, I found that out just now and I smacked myself upside the head a few times when I also realized there was also an UnloadSounds() function right below LoadSounds().
Soooo, I simply reset the the red alert sound in this function to the default sound so everything goes back to normal once I load a new bridge. I'm not sure where UnloadSounds() is called but when I switched between my Sovereign, Galaxy, and Excelsior bridge (which I also have a new sound file for now), everything ran smoothly.
So I guess I don't have to waste my time changing all the other *bridge.py files. 8)
Right now, I only have to change the Sovereign and Excelsior bridge scripts, while keeping the Galaxy script untouched since it already uses the default sound. This works out for the best.

Thanks guys!