I like the way the firefighter hat was handled in destiny. The firefighter hat was updated but not the original file. Owners of the older hat kept the old gfx and could also get the new hat, as well as a special hat. If a similar method were introduced where only owners of the old hats could receive an updated version as a separate hat I think that would keep the peace.

There are some old hats that should not be touched because their identity is that they suck. The first one that comes to mind is hat184.png