I just opened another thread on the editor Use instrument editor to define global percussion playing techniques - #2 by mavros It is related to entering playing techniques for percussion instruments in the instrument editor but I also had the uncertainty what the activated star button really does.
You probably also noticed that the instrument editor works best if none of the instruments you are working on is in the score. If it is in the score the editing options are limited and I am not sure if any changes you make will become globally available even if the star is activated.
Regrading percussion instruments, creating variants will lead to some confusion in the percussion map editor as for some reason it does not show the full instrument name including the variant number. So you will see e.g. three tom (high) entries in your instrument list in the PM editor if you created two variants. The order is not always logical (i.e. default, 1,2 )
What I had also noticed ,but it may have been fixed now, is that your user added instrument turns up in the list when you want to add an instrument to a player but not in the list you see when you want to change an instrument.
The editor seems to be still WIP but it has already improved a lot.