Is it, at the current point in time, possible to change a unit's quotes? For example, let's say I recorded myself saying "sup dude" and wanted to make the SCV say that when clicked on. How would I, if I could?

The WCIII way is to find the audio file in SCII MPQs, import the file in the editor and set the filepath to that of the audio file in the MPQ.

Ya, its a simple mod, but the audio file has to be in correct format(usually a .wav file)

I thought SC2 audio is in the .ogg format...

i think it is .ogg cuz i very highly doubt they would continue using .wav

Yes, Starcraft 2 uses .ogg as the sound file format.

SC2 also uses wav. I know this because I've imported the old observer explosion sound to use in my remake of dodgeball.

The other day someone in the sc2mapster irc also mentioned wav and ogg as being the only sound files supported by SC2.