I'm making a few animations for a character in a racing game, run, walk, die and also a win animation in the win animation I want to add a medal around the characters neck, is there a way to do this in the action editor without making a new mesh with the medal in it?
You can add an intermediate bone, which deforms the medal. On the first frame of the winning animation it will simply have a scale keyframe at
(1, 1, 1). On all other actions you keyframe it to a scale of
(0, 0, 0) effectively hiding it.
Otherwise create a separate object, which the game engine can show/hide.