It probably won’t work well to try to move the diaphragm for breathing. I mean that a person will feel uneasy to breath with this way. The diaphragm is a muscle. It is disadvantageous way to try to move or use muscles. We tend to give excess muscle contraction than needed with this intention. We had better pay attention to its objective of the movement or activity and let muscles and joint act as if they move automatically. (i.e., try not to use them intentionally) This way of intention is called “leading edge”. This is advantageous way of intention.
For breathing, the objective is to move air. We had better think of air as “the edge to lead”, and intend to lead the edge, i.e., move air. In exhalation we had better intend to breath out the air inside from the mouth (or nose) into the space right in front of our face. In inhalation we had better intend to breath in the air right in front of our face from the mouth (or nose). Let the muscles work automatically and let the rib cage move automatically. This intention becomes a matter of course, but we always tend to forget this simple intention of objective. This is simple, but this still works.
Our way of intention affects the quality of our movement or activity, and there seems to be a rule for the way of intention. The concept of “leading edge” has been used by some AT teachers. This is still hypothesis, but it works well so far.