I believe that many people understand that requirement should be freeze and don't be changed during implementation phrase. However, how many people willing do it or could follow this rule? I think it is a good open question.
As many books mentioned, we should not change the requirement during implementation phrase since the cost for changing will be much higher that change it under requirement capturing or analysis phrase.
For the big changes such as adding a new modules, I think many companies have the proper procedure to handle it. But for the minor changes, people will easily ignore the risk and accept the change. Actually, this is the hidden problem to make the system unstable.
Of course, to modify this minor change won't affect the system and it also could make the system better.. But what happen if we continue to do these minor changes under different times? Many people will continue to accept these changes but the fact is, 10 variances will create over 10 x 10 times variances and make the system difficult to maintain. People are easily skip to re-think these 10 variances at same time since it is not under the ANALYSIS phrase.
One of the key point for project management is to make sure everything are under control, if we create so many variances, how could we manage the project properly?
Therefore, please think carefully before accept the change. We need to improve the PM and system architecture and let them to decide even add a field or disable a button.
As I mentioned in this article, disable one button won't make much impact to the system but if we do many of these changes, the system will suffer finally.