Well… in practice this is still not a simple technique. Pressing UU will pull up ALL the modified keyframes. So you can’t simply drag a box around all the modified properties or else you will copy properties that you don’t want as well. Instead, you have to look through a potentially long list of properties and carefully pick which ones you want and don’t want to copy. I find this to be quite tedious.
Copying and pasting keyframes is simple because they are easily visible. Copying and pasting specific modified keyframes however, is difficult because they blend in and are hard to weed out amongst the others.