After rolling one or more six-sided dice and seeing the results, you decide whether you want to make the exchange. You may exchange one result at most, no matter how many dice you rolled. For example, say Vedalken Squirrel-Whacker is a 2/5 and you roll a 3. You could make Vedalken Squirrel-Whacker a 3/5 and change the die roll result to 2, make it a 2/3 and change the die roll result to 5, or leave everything how it was.