I have a few comments to make.
First of all, basketball is a great off season activity to partake in for pitchers in my opinion (as long as you don't get hurt). It's a lot of short distance sprints, and really builds explosiveness while keeping you in shape. Let me tell you a little story that involves basketball somewhat. I broke my leg the summer after my freshman year of high school sliding into third base in a summer league game. I broke both bones in my leg, and fractured my ankle. The orthopedic surgeon said it was the worst baseball injury he's ever seen. I had surgery and had a 12 inch stainless steel plate put in, with 12 screws, as well as pins in my ankle. He right away said I would be out 6 months. I ended up coming back in 4. I went through all the treatments, did everything right, was on crutches/in a wheelchair with a cast for a couple months, then in a walking boot. I did physical therapy on my leg and really pushed to get back. I happened to get out of my boot as soon as basketball season starts, but after being in a cast and walking boot for a few months I still had some issues to work out. I used that basketball season as an extra rehab and worked my leg back into shape. At first when I came out of the boot, it hurt to bend my foot as it hadn't bent normally in several months so I had to work it out. At the end of that season I was running smooth and fine, with a new determination. With the exception of the plate hurting every once in a while as it settled into my leg with screws and such. Here it is about 6 1/2 years later and I'm absolutely fine and still have that plate and those screws in my leg even though I was told it could come out in two years due to the surgeon who did my leg leaving and the new one not wanting to quote, "fix something that's not broke". I no longer have any pain except for after a really long hard run on concrete. I was really hitting my stride with baseball that summer, and the injury grinded things to a halt for me. My legs are now stronger than ever with the exception that I still have a difference in size between my left leg and my right leg, although it's getting better. My point of this long story, is that basketball can be very useful for a baseball player. No matter how it's put. I also used the time I was done to read everything I could get my hands on that related to pitching and made my time productive. (Sorry for the long post, look to the general pitching forum for my whole story that I will be posting after this.)
My second comment is about the changeup. Over my years of pitching (and still now as I pitch in college), I have tried basically every changeup grip out there. I could never get it to work, and when I could get one to work for me it would only work for a few pitches and then I had no idea where it was going. I didn't have a true change up until this year, when I decided to stick with the circle change and develop it. I found the right grip, and figured out what I was doing wrong. The whole time I was throwing it "like it was a changeup" and was trying to make it go slow. But the key is to get the changeup grip, and then throw a fastball. Same arm speed, same arm slot, nothing different. People had told me this, but it never really caught on. Once I started doing that I created the best change up I've ever had. I'm hitting spots with it, as well as getting tremendous movement. During the fall when I was throwing it, I never through it for a ball and no one every put a bat on it. All in all, a big key to pitching is trusting in your pitches. That was another problem of mine. Trust that once you get your grip, and start to throw that the pitch is going to act like you want it and you're going to throw it exactly where you want it.
Again, sorry for the long post, and good luck on your goals! I'm here to help if you need anything.