Yeah, as long as you match the beats up right, you can drop out the instrumental (track 1) at the right moment, bring in the chorus (track 2), and then drop out the chorus again when you want to go back to the instrumental. I do similar things all the time when I have to edit a song for time for some of our weekend programming. Keep in mind that I'm coming from a simple editing perspective, so we may not be visualizing the same thing here.
Either way would work, as long as the totality of the chorus is good for GT's purposes in the first choice. If he didn't want part of the audio in the chorus on his mix, then he has to go with the acapella.
I think I know what you're talking about. You're talking about separating channels, post-mixdown, right? Usually vocals are recorded in the center of the mix, so they can be separated from a lot of the other tracks. But kicks and snares are usually centered too, so a lot of times it's not always easy to separate it. Also, choruses are usually mixed by panning multiple layers of the vocal out to the sides of the mix to create the stereo effect, so that makes it more difficult too.
I've never had much success separating tracks from a mixed down MP3.
Am I right about what you're talking about? You separate the tracks from a final mixed down track, like an MP3 or whatever file type it happens to be?