Animal TO is eligible, you cannot TO Gods, Demons, or Beasts. They're limited. Animal TOs are semi-limited. So you're in luck if you are going snake. Love Orochimaru tbh, better join Grimoire Heart ; D
Yes of course, most spells should be partial. Like tongues, arms, tails, and wings! You can keep an animal form, and your spells can create snake that you throw. But they wouldn't operate like summoning. Just an extension of who you are-- meaning it would have to stay attached and all. Like if your arm turned into a bunch of snakes, that'd be fine. Just remember-- poison is not allowed.