I mean previous in time, not in space. So that defining a variable that already is defined would invalidate the ‘previously defined’ one.
So the ‘current’ definition would be the one in the cell that is being edited (press ‘enter’ or whatever you do), and previous would be everything else.
Anyway, just an idle thought, not a strong preference on my part.
Perhaps the way Pluto reads the file is such that it cannot tell the difference, that it builds the ‘graph’ all over, for each edit? In that case I see that it wouldn’t be doable.