Can I have my pinky finger lengthened? I want to play guitar and it makes it a nightmare

Doubtful. That is a very very very painful procedure to lengthen bones and may take years even. It is usually done when one leg significantly shorter than the other. I don't know your age. If you are still young, your hands could still be growing. Perhaps in the meantime, you could find an easier instrument to learn that doesn't require as long of finger stretches.
Not likely. I suppose if you are very rich, you could find a person to do just about anything - especially if you sign papers waiving their responsibility - but it would probably not help anyway. Talk to lots of guitarists for better ideas. They can be fun to talk to if they want to.