If it was near the end of the run, it wouldn't be the first time; two other "last-minute" changes I remember are Celebrity Sweepstakes getting rid of having to write down answers in the main portion of the game, and Monty Hall Beat the Clock having both couples perform every stunt in its final two weeks.
That's the first I've heard about Beat the Clock - thanks!
As to CC, once they switched to the 2-out-of-3 match, the main format was rather steady for two years. I don't think it's quite out of step with other Goodson shows. As mentioned, Trivia Trap had tweaks...by week two, to speed things up, they were already doubling the Trivia Race questions to $200 after 10 were asked.
I think the fact Concentration's format lends itself to so many different things in and around the game - just like the original NBC version - is why they bothered tweaking at all. To put different things on the board isn't near the trouble as introducing new rounds, changing camera blocking, etc. It has to be the same reason Price was tinkering so much in the first few years, daytime & nighttime. They weren't married to games being in one place on the set, just for one example, so why not try new locations?
-Jason