2022-10-07 : 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.

2022-10-07 : If Vedalken Squirrel-Whacker’s base power or toughness changes through some other means, it is possible to exchange a die roll so that it has a result that would normally not be possible for that die, such as, on a six-sided die, a result of 9, or 42, or -3. These are all perfectly reasonable results on a six-sided die.

2022-10-07 : The two die rolls to set initial base power and toughness are separate and sequential. If you want to reroll the first die, you must do so before you roll the second die.

2022-10-07 : Vedalken Squirrel-Whacker’s second ability functions only while Vedalken Squirrel-Whacker is on the battlefield. Specially, the second ability can’t affect rolls of the first ability.