In that respect you shouldn't be able to edit the map either, probably brings more to the table than a trap sprite. Why allow one and not the other? That I don't agree with.
I think maybe a slap on the wrist would cover this issue, not like he's changing the world by having edited ankle snare sprites. His targets are same size, the traps are also the same size, and nobody is a giant monster on his screen. No issues imo.
Slap on the wrist. A simple, "hey, don't ever use that again." is fine. If he was using nodelay or something along those lines, sure. But this is a trap sprite.
I dunno how long the ban is, but I think a temp ban would suffice for this. Gives him enough time to download and install a clean client and go about his business until he can come back to the game.