I'm sure this has been discussed earlier but wasn't able to find the topic so...
I want to change the instrument on one realtrack for another instrument while keeping the notes being played.

I open a style (e.g. _slblgrw.sty) and I want to change the "Guitar 1" (822: guitar) realtrack to a "1124 fiddle" realtrack but still keeping the notes played by the guitar. What is the procedure to do this?

What I've tried is to right-click on the track in the mixer and selected the fiddle from the "Best all Real tracks". This results in
1) the instrument name in the mixer changes (OK)
2) the notes shown in the Notation window changes (not OK)
3) the melody played on the track remains the same as the original, i.e. not what is shown in the Notation window.

How to do this correctly?