Again, I'm not understanding what you want, can you make a picture or website where you are actually seeing these levels?
Here is how you can make the Fibonacci Tool draw levels both above and below the measured range, as shown.
The Expansion Tool could do the same, so please tell, what are the targets on Harmonic patterns that you desire?
Here is a stock standard application of the Fib Expansion Tool, as you said, it gives the C to D projection using the range A to B.
If you can do a chart showing the range that you want measure, and where you want the lines projected to, extend or retrace, very simple.