I would like to forward something a member of my coven posted about basics. It includes how you can modify anything to suit your needs.
If you want to cast a spell, but see something that you don't like the thought of doing, such as cutting yourself to add your own blood, try substituting it somehow. Add something that fits in with the spell and should have the same results. The spell may not be as strong, but it should still work. Just be sure to ask your peers about what you're doing to ensure you are adding the best possible substitute. You may find that it might actually be better to just drop that specific ingredient without a replacement for it.
I hope that this will help you.