sometimes I forget to change the instrument-slot (I want to add another VSTi) and all settings are lost … maybe a confirmation dialog would be useful > “really?”
… but this confirmation should only be displayed if the current song contains notes of current instrument in the slot …
Doh! 
how about “undo”?
i do this all the time.
I’m an idiot, tho.
happens time after time here 2 
Undo 4 this should be super-great !
in those (luckily rare, for me) situations, I load up another session of ReNoise, pick up an automated backup of the song (saved each 10 minutes), save the lost RNI, and load it into the song