If anything, give to Kyurem-Black all the Electric moves and to Kyurem-W all the Fire moves. Which at the end of the story is only Bolt Strike and Blue Flare, respectively. Volt Switch Kyurem-Black maybe.
Idk, if you are on the fence about changing things i would rather give to in-battle alternative forms their stabs, and it would make sense since the actual movepools are specifically desinged for these forms(think about Close Combat Meloetta, Psychic Darmanitan or Dragon Pulse Ampharos), but aside from the massive buff to Gyarados(Foul Play, Knock Off, Sucker Punch, Parting Shot, Dark Void, on top of Brave Bird, Defog and Roost) things wouldn't change too much. Meloetta may have Aura Sphere, but she already had Focus Blast anyway, Trick gives to Darmanitan 4MSS(should I forgot Earthquake or U-Turn for this?), Draco Meteor/Spacial Rend Ampharos is cute, but far from game-changing, Charizard has already any Dragon move it could wish for, Mewtwo is banned and no one cares about Castform suddenly gaining Crabhammer, Sacred Fire and Icicle Crash.