Still Unsolved: Make enemies attack other enemies

I want to create a certain item that, when you hit an enemy with it, the enemy becomes temporarily passive to the player and hostile to other enemies.
How would I go about this? I did some searching and while I could technically just make an entity that replaces whatever hit, I want this to be compatible with mods and I don't want to replace the entity hit with my own. 
Would it be possible to do this using scoreboards??