A lot of researchers would disagree with the statement "That’s not how science works: You don’t sign a contract to not change anything in your protocol as the research evolves" You've got to complete the test using the protocol and hypotheses established at the outset. If you decide a change in protocol is required you wrap up the original test, report on the results, and then start a new test. Otherwise you end up with some combination of the issues described in A menagerie of messed up data analyses and how to avoid them[1]

[1] http://simplystatistics.org/2016/02/01/a-menagerie-of-messed...