I was just going through some old posts of mine. Thought I could improve them just a tiny bit. I have no intention of bringing them back onto the "active questions" feed. How do I edit them, yet keep them away from the feed?
As @sumelic notes in comments and via the offered link, there is no way to edit any post without bumping it to the active questions feed.
I understand SE's philosophy on the matter to be that improvements to posts are encouraged because the site is intended to be a repository of expertly answered questions. The community goes to great lengths to review, edit, vote and cull questions and answers for quality. So if you can raise the quality of an old post, it would be consistent with Stack Exchange's philosophy for you to do so.
Editing is important for keeping questions and answers clear, relevant, and up-to-date. - help center