Musical Score

Instrument changes are not well supported right now. There are two methods you can use, neither ideal.

Probably the best for most purposes is to have each instruments separate in the score (eg, if one person plays clarinet and flute, have those as separate staves in the score), but set up the parts so that both clarinet and flute staves extract to the same part. You can then use Hide Empty Staves to make sure the instrument not being used doesn't display. You'll have to make sure the instrument changes happen at line breaks or you'll see some systems with two staves.

The other method would be to create scoire using just instrument, but manually transpose the parts where it supposed to be played on another instrument. It won't playback correctly, of course, but it will look better in the score, and extrracting parts is simpler.

What I've done is create the score using separate instruments as in the first approach and use that for playback. Then when I'm satisfied I'm done, I save this score to a separate file. I then copy/paste the doubles to their proper staves, eliminate the original staves for the doubles, and do the manual transposition, then extract parts from there. I now have two copies of the score - one that works for playback, the other for print. If I make subsequent changes, I have to decide if it's worth making them to both copies.

For 2.0, MuseScore will support an "instrument change" text type that will make playback correct, but as of last I checked it doesn't update transposition, so it's kind of useless except for concert pitch scores.