Joker's Wild had a slew at the beginning of its life. $150 triples, no question on three jokers, circles around prizes, car on the wheels, 4 wins to get the jackpot, 4 prizes in the jokers/devils game....
The first two, and "4 wins for the jackpot," lasted for the first 10 episodes (something I never would have known had WCBS(?) not discovered the tapes and GSN converted and aired them). The "circles" end game ran for I think just the first two shows, after which the car (and once that was one, a trip to Mexico) was put directly into the game. (Anybody remember how long the "leave the show or risk all of your main game winnings" rule lasted?)
A few more to add:
TPIR: in the Dennis James version, originally there was a $1000 bonus (briefly) if you won both prizes in Clock Game and had more than 2 seconds left on the clock.
Celebrity Sweepstakes had a number of changes, but the only two I can think of that might be considered "short-lived" were (a) originally there were three contestants instead of two, and (b) at the end of the show's run, they got rid of having to write down answers before the Homestretch round.
Beat The Clock (Monty Hall version): in the show's last two weeks, both couples played all of the first four stunts (other than only the winners of the first and third stunts playing the second and fourth ones, respectively).
21 (the relatively recent) version changed its payout structure a number of times in a brief period. The ones I remember were, for each game won:
a) 100K, 200K, 300K, 400K, and then 500K for all wins starting with the fifth;
b) 100K, 200K, 300K, 400K, and then repeat the cycle;
c) 25K, 50K, 100K, 250K, 500K, 750K, 1M, and then repeat the cycle
(I'm not so sure about how brief this one was) Beat the Odds: in a handful of episodes, one of the two "exactly 5 letters" spaces was "7 letters or longer."
Also, how soon into the revised version of The Joker's Wild did they switch from having dollar amounts in the main game to categories?