How can a texture hack work?

[SchadowCloud]

Wuzzsup

So I was pretty annoyed by all the ambient sound in MW2 , so I checked out the sound files in my main folder. I found some sounds like the
phone call or the jet sound from terminal but when I removed them or edited the file it kicked me with the error "Files diffrent from the server".
Well today I tried to insert custom skies but I got the same error and I was woundering how you could use a texture hack then?
I mean texture hack just puts diffrent files in the files of the main folder to get something like a red enemy and you do the same with
custom skies, so why is it accepting those texture hacks and not those custom skies?
And after all is it possible to edit the sounds? Still annoyed by dat ambient sound :/

Thanks for the help

// Aint wanted to have that smiley as prefix lel