It can be added to any spell, it is your will that you cast with, now you are adding an earth element of a pure form concerning the river of blood that runs through you, we are made up of water and bone, dense muscle and sinew, this is all stable in our design, except blood. It flows and moves with our emotion, it is the only thing that keeps your heart alive when it is broken like a shattering glacier.
Allways remember, the law of return, blood is powerfull, when you cast with it, you draw it down into your karmic flow, there is the three fold law of return, and at times the seven fold law.
And dont think, 'and may it harm none' will overide the strength of the blood, your intention guides the magic, this is what the universe hears.
So it is up to you really, if what you decide is so important that you feel the need to use blood, what you do along side this, the words you speak, the forces you invoke, thats what can get you in some trouble
If you are knowledgable enough to steer this the way you desire, with no adverse effects, covering your negatives with the insight that every thing is now crowned with the empowerment of your blood will, or as my name implies bloodwish, then :)) have fun!