So I kindly sent my wish to the developers and got an honest answer, thank you Renoise team
(Basically liking the idea, but have to implement it in a way that lots of people stay happy).
I just found out by accident that when pressing the middle mouse button on a selection, it plays thát selection.
But then again, it does not correspond with the keyboard, but it is a hint to what I want.
I think, I will write macro’s in AutoIT to quickly do a trim and undo, although that is not the nicest solution.
Maybe I will map the middle mouse for trim, and press again = undo.