Yes, these things are possible—and it all has to do with “The Secret”, which I learned many moons ago. And what that secret is—is getting your whole body into the action and not just throw with the arm and the shoulder. You drive off the lower h alf of the body, using the legs, the hips and the torso in one continuous (and, I might add, seamless) motion, and in doing so you generate more power behind your pitches. This use of the lower body to start a whole continuum going is the real key to a pitcher’s power, and in doing this you take a lot of pressure off the arm and the shoulder so that you’re throwing harder and faster with less effort. I learned this from three Yankee pitchers who were doing this all the time, and I saw just how they were doing it, and I made a note of it and started working on it on my own. I found that even though I was not, and never would be, very fast I could throw harder with less effort, and somewhere along the line I even acquired an 81-MPH four-seamer which, for a finesse pitcher like myself, was a fast ball. There are several drills and exercises you can do to this end; one of the best is called the “Hershiser drill” which aims at getting the hips fully involved, and you can find it and some others on this website and also on the NPA site.
The other thing you’re asking about is how to throw a changeup. There is a whole closetful of them to pick and choose from, and basically you can do this with different grips, by holding the ball well back in the hand or further forward—but one thing you have to remember: you have to throw all those pitches with the same arm motion and the same arm speed as you would for a fast ball, because one thing you do NOT want to do is telegraph them! And—this goes for everything you throw—you want to throw from an arm slot that is comfortable for you. My wise and wonderful pitching coach, an active member of that Yankee pitching rotation, firmly believed that every pitcher has a natural motion, and what he would do was work with that pitcher and show him or her how to make the most of it. (I was a natural sidearmer.)
Well. these are some of the basics. Any more questions? There’s a whole bunch of us waiting to answer them. 8)