It would be extremely helpful for modding purposes if we could create objects that act like levers but use a custom sprite.
I agree with this idea. Although I do acknowledge that a work-around for this is possible right now; it merely isn't one a "basic" user is likely to know how to use (though that can be enough for such a change).
What's the workaround? I had a couple ideas involving customblockers that are rebuilt by the script, but I don't know if there are any others.
That's pretty much the gist of it - use something, whether it's traps or customblockers or anything else one can get to work (right now, "anything else" consists of spells effects used to make passable animations of this sort and to juggle buffs). Of course, in most cases these work-arounds won't result in actual levers but rather something that it equivalent to a lever (and is thus an on/off switch) and it's hardly elegant, but that is why I am not saying "everyone should learn how to do it" and instead support your idea.