If I add a new branch to an existing one then adjust so there is only ONE new branch, is it possible to revolve that one new branch around its parent branch?
You can not do that directly (as far as I know). There are two workarounds though:
On the parent branch adjust the RotAngle. This spins the branch on it’s longitudinal axis effectively. If you are using any Axis variation on the parent branch, however, this may or may not be a desirable option.
Set Density in the Branching tab so that you get two branches instead of one. Then on the Stem panel use the Offset influence curve to suppress the lower branch. RevAngle will now rotate the remaining branch around the parent stem. Depending what other parameters you are using, this option may behave somewhat unpredictably.