While the track is playing, any changes made to the current instrument should be applied in real time (You can still start/stop the song with the instrument editor open). Is this working for you?
I plan to implement a way to hear the instrument by playing it from the keyboard.
That's my concern - I had a pattern playing and was turning various operators, but no new sounds were being made. I left the synth screen, then there were changes. I don't play the keyboard like most folks, just to enter the notes when I need them. So, I made the pattern, then went to the synth page to adjust the sound, but I didn't hear any changes until I went to the pattern again.
The sequencer changes the instrument only when it plays a step with an instrument value set (the second number in the row).
You might need to open the instrument editor twice: once to assign the instrument (making sure the instrument number is displayed in the pattern), then reopen the instrument editor again to tweak the sound.