Our deepest fear is not that we are inadequate. Our deepest fear is that we are powerful beyond measure.
35.22 and 35.23 does not mention pivoting limitations in regards to the Advance
That's because those rules have nothing to do with the Advance order; they're in the Move order section.
(by the way, you meant 35.21 and 35.22, as 35.23 has no such limitation)
does the free change of the fire arc for a gun under the Advance order allow for more than one "hexside" change
Yes. *All* pivots can be made to any hexside desired unless specifically limited (for example, the limits given in rules 35.21 and 35.22 during a Move order).
Have fun this weekend!