Splendid! The Split tool worked perfectly, thanks. This is exactly what I was wanting to do. The Split At Selection in the Split Clips box is the one.
The Undo History seems to only work with the top Process menu, Apply Effects - Remove Silence, Gain, Normalise et cetera. But if you right click in a selection, Process Effects, Audio Effects, any effect will not be recorded in History. Only the word "Undo" is displayed. And yes, you can undo them. I thought it was my old Sonar 8 VSTs, but it applies to all effect in this version too. The effects name will not display.