I think this is getting away from the idea of a rule or format change from a fluke incident setting a precedent. A lot of examples given are just rule changes...an all-celeb format is usually nothing more than a last-ditch effort to boost the ratings (using the most recent example given).
It's not quite a rule/format change, but wasn't the Press Your Luck board pattern changed dramatically following Larsongate? Same reason Whammy's pattern was randomized?
I also seem to remember reading about a rule change in Win, Lose, or Draw's bonus round during the Robb Weller era. From what I remember reading, the original rule was to start out with the first word worth say, $100, then doubling from there. Apparently, one early contestant went on a tear and racked up about $25,000+, prompting the producers to make it 7 in whatever time period for $5,000.
This was prolly posted in the ATGS era, so I'm going off a 10-year-old memory here. Forgive me if it's nothing more than just urban legend.