Oh, you probably also want to know why.
Well, with Aggron ex active, it shuts down all Basic's Powers and Bodies.
So, when Dialga G X comes into play, it's Body is off.
Switching one Aggron for another doesn't matter. The switch, in game time, is instantaneous. As far as the game is concerned, Intimidating Armor was in effect constantly.
Not that it really matters, though, because what you are asking about is whether Rain Dance works.
Rain Dance, on Blastoise, is a Pokemon Power, not a Poke-Power. However, if an effect that shuts off both Poke-Powers AND Poke-Bodies affects Blastoise, that would shut off the Pokemon Power since the two of them comprise Pokemon Powers (see rulings in the old Compendium on this).
Anyway, of all things in play, what could shut off Rain Dance?
Well, Dialga G X only shuts off Bodies. So that wouldn't shut off Rain Dance.
Aggron ex only shuts off things on Basics. Blastoise is not a Basic, it's an evolved Stage 2.
Muk ex would shut it off, but it has to be active for it's Body to work.
It's on the bench.
So, the whole thing about switching off the Aggrons is a red herring.
