Forever Changing is an achievement in the S.H.I.E.L.D. Missions category. It is worth 30 Gold Nuggets and is a secret achievement.
Forever Changing: ???
Behind one of the moutains on the eastern side of the map is the Chameleon's cliff hideout where his masks are displayed on poles. Taking one of the masks to the Tech and Research Centre, the scientist will research it ability to change voice and allow optical camoflague, applying it onto any further masks you find within 1 in-game day.