1. Yes, you can inject into any muscle.
2. Yes, speaking from personal experience, the injection I did in my calf was one of the most painful experiences I ever went through. I could barely walk for a week.
Site injections dont work. That's total bro science. As soon as you inject a steroid into a muscle, it is dispersed into the blood stream and flows throughout your body to perform it's mechanism of action. Stick with easy injection sites like glutes, quads, side deltoids etc.