As the title says, is it possible to register an Icon from another mod's assets using a ResourceLocation? I haven't found any way looking through the Item methods. Would I have to make a custom renderer to draw the Icon instead of using getIcon(...)?

	this.setTextureName(ModInfo.MODID+":itemLime");

I am not sure it works, but i think you have try to change MODID to other mod id.

getIcon() will still work fine. However, instead of using the unlocalized name for your item use: modid:texturename where modid is the mod id of the mod you want the texture from.