Here’s a research article tackling the same problem of changing outcome measures after the data is collected. Apparently, this occurs in 66 of the 226 papers reviewed here or almost 30% of the time. The interesting thing is that whether this occurred or not was independent of whether paper was accepted. So journal editors are missing an opportunity here to improve the quality of the published literature by demanding that researchers abide by the choices that they made during trial registration.
van Lent M, IntHout J, Out HJ. Differences between information in registries and articles did not influence publication acceptance. Journal of clinical Epidemiology. 68(9): 2015 (September); 1059-1067.