An Animagus transformation is a very difficult and lengthy process in which to learn. Though, I am please to find that you have an interest in learning more about such a branch of Transfiguration. I could point you in the direction of several books that provide and excellence explanation of the deeper theory behind it. Yes, it is important to know the whole theory behind such a thing as it is very dangerous and could go terribly wrong.
I learned my ability after an extensive training, for several years, with Professor Dumbledore and many other accomplished witches and wizards in the field. As for being sanctioned, there is a committee one must register with within the Ministry in the Department of Improper Use of Magic. Where you must reveal your Animagus form and consent to being listened on the public register.
As one of my more gifted students in the field, I offer you this: complete the attached list of reading materials the best that you can over your remaining summer vacation and when you return to school, if you are still interested, we can arrange to further your studies in with practical experience and lessons to see if you cannot learn this branch of magic. The condition is that you keep your grades up through out the term.