Do you mean the sounds or the actual emoticon?
If you want to change the emoticon just type /skiss (or any sound)
or wahtever.
If you wanna make new sounds you can go
Here and download the audiator 3 plug in and go
Here For help about it. (FAQ)
***your contact must have this plug in install to hear the sounds aswell***
Edit: and you could probably make quick text with it...like, it if were a sneeze, make a custome emoticon sneezing (kinda) and then add the sound to it...so like "/sneeze
*achoooo*"