Playback

That is possible but not an intended purpose of voices and the mixer. To do this, it takes a little bit of trickery.

Create an instrument with 3 channels like the violin. It give you a sound for Violin, Violin-Pizzicato and Violin-Tremolo. If you can't see these channels, click the arrow at the top left of the box for the instrument. You can then select each channel one by one and change the sound of the channel to any instrument you like. Do this for each of the three chanels, but keep in mind you cannot have instruments with different transpositions display and play properly on the same staff like this. So you can have a Flute, Oboe and C trumpet on the same staff, but you can't make one of these a piccolo (because it transposes 1 octave), a Bb clarinet, English horn and so on. To be clear, these transposing instruments display the notes on the wrong staff lines. Keeping this in mind, once you have assigned the sounds to the channels, insert any text you like, meaningful text is better, but you can make meaningless text invisible if you like. Right click the text you entered and choose "Staff Text Properties..." There are 4 buttons to show which voice you are selecting for a sound. Click the 1 and in the dropdown select "Normal", on the next line click 2 and assign "pizzicato" to it, on the third line click 3 and assign "tremolo" to it. The instrument you assigned to violin will sound for all voice 1 notes, the instrument sound you assigned to violin-pizzicato will be in all voice 2 notes and voice 3 will have the instrument you assigned to violin-tremolo.

This sounds much more complicated than it sounds, but is quite easy once to understand it. You will very likely end up with red or gold notes because the violin does not have the same range, I would suggest that you open Edit(MuseScore on Mac)->Preferences and under the Notes tab uncheck "Color notes outside of usable pitch range" if you run into this problem and don't like it. There are other ways to fix colored notes, but this is the easiest.

Feel free to ask further questions if I didn't make something clear.