Mark, on the precedent question: one mistaken approval generally doesn't rewrite a four-foot limit, though a pattern of exceptions can change things, as ElleN said. Before deciding what to tell this owner, I'd pull the original application, drawing, approval letter, and meeting record. Did the application clearly say six feet? Was the approval unconditional? Those details matter more than a later recollection that somebody made a mistake.
The "leave it until replacement" approach may be worth exploring, but I wouldn't present it as automatically enforceable. Have the association's attorney look at the actual approval and the owner's reliance on it before promising an exception or demanding removal.
For future applications, add a comparison sheet: proposed height, declared limit, and the exact source section, with the approved drawing attached to the response.
Before pursuing removal or penalties, have counsel identify any required notices and hearings under the applicable law and your governing documents.
ā Eli