Hello! The only time I've heard of someone applying as a junior and being accepted was one of the vets I shadowed. She went to a school where there was an accelerated animal science program, finished her degree in 3 years, and then went right into the vet school at the same university.
That said, I don't think it's a very common thing, though it does happen occasionally. I think it's wonderful that you absolutely know what you're going to do with your life and I understand the want to get there as quickly as you can. However... to me, college is an important part of the growing up process. I think it's your last easy opportunity to explore any other interests you might have, learn things that aren't necessarily veterinary related, and grow as an individual before you get to vet med. Vet school will be all consuming, and I'm very glad that I spent a lot of my time in college doing things that weren't playing with dogs every day or reading an anatomy textbook (though I adore dogs and am actually looking forward to anatomy [don't burst my bubble]).
But that's just me... I wanted to be a vet when I was 6 years old, and in college I had a few mini-crises where I changed my major several times and tried any and every other field I had even the remotest interest in. Ultimately, I believe you end up where you belong 🙂 Best of luck!
Edit: oh, and the other part of your question - I think any time you reapply to vet school, you should rewrite your personal statement to reflect how you've grown and changed and what makes you a better applicant this time around.