In the sample editor, in a stereo file, is there a way to select one channel only? ie left or
right only
I don't think so. I think you have to go through a big hassle, and change your preferences to force separate L and R then save the file, then change prefs back, then reopen the L or R file alone.
When I am recording guitar with two mics, instead of recording stereo, I record mono to two separate tracks. Then time correct the start points of each, and you don't have to worry about phase and all that.