Maybe what you do is create a duplicate of every playable race. Then in each duplicate race edit and add the knockback effect to each power attack you want the Perk in theory to effect. (make sure to edit both sixes)
Then go and create a silent spell (a spell with no description and no 'Name') and also add a silent Magic Effect (that the spell uses) which does nothing more then apply the Perk you've created. (Essentially the Perk is doing nothing but here comes the catch).
Now you create a quest that does nothing more then add this new spell to the player and changes the players race to one of the duplicates you created. (similar to how the vampire script checks to see which default race you are playing then switches you over to its appropriate vampire race when you change into a vampire)
Here's the part I'm not sure of.
There should be a way to have this new quest you created added to the player when the player gains the Perk. I believe either through a quest stage or through perhaps an alias?
Just some ideas. It's how I would approach the problem. Im no CK expert though. Just a noob
