Well, it will be handy if png can be redirected.

Check my case. I wanted to use Sandris's HD spell + Reinforcement Spell (a spell mod replacing disguise, with a new icon). Since Sandris's spell is in PNG, I created reinforcement spell graphics also in png and set conditions - when reinforcement mod is loaded, load these new pngs instead.

Without png redirection support, I have to create two sets of defs frames with exactly the same pngs inside (except Reinforcement) for the condition with and without reinforcement mod. It can be done, but isn't in an efficient way.