How do I change the instrument on a realtrack without changing the notes being played on the track ?

I can change the instrument in the mixer by right-clicking on the patch, so far so good. However, when I press the PLAY button the old instrument is played (despite that the new one is shown in the mixer). If I re-generate the track the new, correct instrument is played, but also the notes which I want to keep.

If I freeze the track neither the notes nor the instrument is changed, an expected behaviour.

What is the correct procedure to change the instrument and keep the notes (melody) ?

I'm using
Version 2020, 734