Adding / overriding glyphs

I have a two MM fonts with four masters.

I want to override some glyphs from font1 to font 2.
On all of the masters.
What is smartest way to do it?

I know I can assign background from one font
to another and swap it, but there have to be
some better way to do it.

Why not Copy & Paste or Paste Special?

Of course - Paste Special, thank you.