Although Mutavault has all creature types while it’s animated, it does not have the changeling keyword ability.

A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of his or her most recent turn. It doesn’t matter how long the permanent has been a creature.

Examples of creature types include Sliver, Goblin, and Soldier. Creature types appear after the dash on the type line of creatures.