Technically I suppose it is a tweak, as it is using a free food in a different way. But normally tweaks refer to tinkering with things like potatoes or chickpeas or lasagne sheets which are relatively high calorie items - OK as part of a balanced meal but a bit dangerous as snacks.
But kale? So few calories in it that I wouldn't worry about it at all. You'd have to eat mountains of it to make a difference.