When a musician is required to double on a different instrument for a section of a piece, the instruction to switch instruments is generally placed above the staff at the beginning of that section. A return to the primary instrument is handled in the same manner.
In MuseScore, the instruction to change to a different instrument is handled by the Change Instrument text element, which is found in the Text Palette. This text element is different from Staff Text, System Text and Expression Text in that it is linked to playback, allowing for a change in sound to the new instrument.
To add an instrument change:
The instruction to change to the new instrument will appear above the selected insertion point in the score.
To remove an instrument change, click once on a Change instrument text element to select it, and press either Del or Backspace.
You can re-label any Change instrument text element in the score by double-clicking on it and entering new text. This will not affect the playback sound of the new instrument.
Playback sounds for instrument changes are reflected in the Mixer as separate channel strips stacked to the right of the primary instrument channel strip. These instruments are labelled in parentheses. You can change the assigned playback library, apply effects, adjust the volume, and mute, solo, and pan these channel strips just as you would any other instrument channel strip. For more information, see the Mixer.