Related to this question, is it feasible for users above a certain rating to be able to remove the 'This question may already have an answer here: [link]' panel. For example, I know my recent question is not answered by the recommendation. It's now a very prominent part of the question and is not helpful (to me or future visitors) for it to continue to appear and it may disuade people from engaging with the question.
Close flags do age away. After a certain amount of time / number of views, the close votes will be removed and you will no longer see the banner.
Other people only see the banner if the question has actually been put on hold or closed. Should that happen, you could edit the question to clarify why it is not a duplicate. This might not be a bad idea anyway: if one person has misinterpreted your question, making it clearer is probably a good plan. Questions that are edited after closing (being put on hold) go into a reopen queue where we can vote to reopen them if it's clear they should not be on hold any more.