Can I ask how I might go about doing so?

i haven't thought about it, but i don't see why it wouldn't work.

Something I've been trying to do is have each L4D1 campaign play their own different zombat music, specifically the horde drums, my method works on local servers but not online. Would it be possible to add custom zombat and have it work online with this mod?

yeah. that's possible.
You could replace the content of all the various zombat sound definitions with the same thing, so that all of them essentially play the same sounds.

I wonder if this possible to make all map play only 1 zombat music file? So that i don't have to replace all zombat music to custom music or something

Good luck, have fun 👌

No, sadly not.
You can only have one script active that edits a specific sound.
But you can make one sound entry load multiple soundfiles using "Rndwave" instead of "wave".

Example:
"Bat.Miss"
{
"channel" "CHAN_WEAPON"
"soundlevel" "SNDLVL_NORM"
"rndwave"
{
"wave" ")weapons/bat/bat_swing_miss1.wav"
"wave" ")weapons/bat/bat_swing_miss2.wav"
}
}

that might work. but if you're gonna unpack the mod anyways, might as well get the cache there

I'm talking about having a sound.cache packed inside the mod .vpk, the soundcache was generated beforehand with snd_buildsoundcachefordirectory referencing only the files used by the mod. That way the sounds and cache is neatly packed away and would never have to be touched by the end user, only the script would require manual installing.

you can only have one soundcache per "content folder"
so either you remake the soundache all the time, or you keep making new folders over and over again just to have more soundcaches

Is there any known limit to the amount of soundcaches that can be used?
Unless I'm missing something I feel like the process could be simplified a bit by having mods include a soundcache for any .wav sound they use, instead of unpacking and making one big centralized cache.

yep. you can just add a new sound event to the firing sequence and make a soundscript entry for that. but i think l4d2 has leftover shell sounds already.

do you think this could be used to make shell sound effects when firing certain weapons?

you could. as long as the game isn't forced to cut it short like saferoom music and death music

With this can i use a 4 min music for escape song? Skinonourteeth

I won't use this, but I must say this is very much needed for many sound mods, and for that I will give it a thumbs up. Thanks.

genius