There is no "non-violence principle" in Epicurean philosophy...
I would argue that there are no such absolute principles in Epicurean philosophy of any kind - there are simply sets of circumstances which you must navigate and ask yourself always "What will happen if I engage in this course and what will not."There is no absolute morality of any kind in Epicurus other than that Nature gives all living things the goal of pursuing pleasure and avoiding pain. There are no absolute rights and wrongs that apply to humans any more than in the animal world, where killing is a way of life.
There are many absolute ideals that are created in society which have a skewed approach to Nature's goal of pursuing pleasure and avoiding pain. For example: there is a kind of rule (but not a law) of "don't wear your shirt backwards" and you could say that doing so doesn't cause much pain to yourself or to others. Then there are religious rules such as for Christians it is "wrong to have sex before marriage". These two I think are skewed (or off) in that they point to moving toward pleasure and avoiding pain, but only in rare circumstances.
Then moving to laws of the land which are firmly established: is it wrong to kill a person unless there is some extreme case of self-defense. I would assert that this should be held as an "absolute law" but it exists because of the rational thinking mind and it is based on Nature's goal of pursuing pleasure and avoiding pain. Knowing that if someone were to try to kill me, that it would be very terrible and very painful and something I would not want, then I take on the idea of this as something to not do -- so this is the "golden rule". (The golden rule is do unto others as you would have done unto you or don't do what you wouldn't want done unto you).
Then going further there is the "platinum rule" which is a variation of the "golden rule". Following the "platinum rule" means thinking about and checking with people to know how the people around you would want to be treated. The platinum rule asks that you: "Do unto others as they would want to be done unto them." But again this is all about Nature's goal of pursuing pleasure and avoiding pain, and thinking about and checking in to see what others would want.