If an attacking creature with double strike and trample destroys all of its blocking creatures with first-strike combat damage, all of its normal combat damage is assigned to the player, planeswalker, or battle that creature's attacking.

Temur Battle Rage checks whether you control a creature with power 4 or greater as it resolves. If you do, the target creature has trample until end of turn even if you no longer control a creature with power 4 or greater later in the turn.