Oops!  That is easier!  What I meant by the needed change "isn't too obvious" is that I thought my code would have a line that says "rotate_bond(bond, angle)" and then I would change it to "rotate_bond(bond, angle, move_smaller = False)".  But in fact the code makes something called a BondRotater in one place (when the mouse is pressed) and later when the mouse is dragged uses that BondRotater object br.angle = new_angle.  This just required a bit of digging, especially to make the more useful code modification that allows you to control which side where I needed to find out how to change the BondRotater to rotate the side closest to the button click (where I don't care which side is smaller).

  None of that was meant as a critique of the code.  I just wanted to warn anyone new to hacking ChimeraX that this isn't the simplest possible kind of change, like changing a False to a True somewhere.

Tom