Speaking as one who dynos street and racing engines on a regular basis, no. A properly built engine will produce very close to its best after about twenty pulls on the dyno. Even then, the difference between first and last pulls is less than about 2-3%. That doesn't include changes from optimizing timing and jetting.

I've dynoed the same engine package year after year in a very competitive class and other than the incremental changes that I've made during the development, there has been very little change.

If there were large changes after break-in, engines would be run longer during break-in before tuning. The engine has to be tuned when producing its maximum power.