And if there is a change of username, there should be an announcement of request so the community will not be surprisedd of that username having their feedback on that account.
People usually change their username due to privacy reasons and making such announcement would defeat their purpose.
If you posted a feedback for a user and the user changed his/her username, it shouldn't be difficult to find out who he/she is.
It is ill-conceived to change your username to cover anything including your privacy, even the weakest searcher on the forum will still be able to know you through a mere forum redirecting unless the person does not remember your username. Some people are so determined to the point that they have enough links and bookmarks on their gadgets. I wonder how it will be difficult for them to locate any user simply by changing their username. The only genuine and reasonable reason I know for such a chance is to reflect what you currently want, our mood changes, and so is our mindsets.