Magic the Gathering Commander Question?

So can your commander be unsummoned or bounced back to your hand or not in this version of the game? One More question also, say my opponent has a creature that says sacrifice and it deals damage and you use an instant such as lightning bolt, can they say that in response they are going to sacrifice it or tap and use its ability making the lightning bolt miss? The same question with land if you try and use a permanent destruction instant to destroy a land, can they tap it and add it to their mana pool before it is destroyed?