I've been trying to organize a lot of retagging on Mi Yodeya and I feel bad that it messes up the home page due to every retag appearing on the home page. Does the stack exchange system afford a method of retagging without causing posts to reappear on the home page?
I had looked up many of the related questions on Meta Stack Exchange and found that
- there is a moderator tool to merge two or more tags (here)
- there is no way to retag questions without impacting the home page (see e.g., here and related links at the end of the question)
- others had previously proposed solutions (e.g., here) but they were not implemented
Therefore it appears the accepted etiquette is to propose tag changes in Meta and, if accepted by the community, proceed with them.
I am personally disturbed by mass retagging like you have recently implemented it because it disturbs the home page with two specific impacts: (1) a new user would see groupings of old questions on similar topics and might be turned off (if only by the lack of variety) and (2) recent answers get buried way down the list and don't get the visibility they might deserve.
My suggestion, if you wish to proceed with mass re-tagging, would be to have a discussion on the content (i.e., the questions/tags you believe merit change) so the community can weigh in whether they feel the gains are greater than the losses.
The fact that changes in tagging (or any edits for that matter) appear on the homepage is deliberate. This guarantees (in theory) that any edits are seen by other users, and any necessary actions can be taken. If edits didn't appear on the homepage it would be possible for a single user to edit hundreds of old questions with inappropriate edits without others catching on.
Additionally, having old posts appear on the homepage can have other benefits as well. Maybe a user who wasn't around when a question was asked five years ago has a good answer. That user might never stumble across the question if it hadn't appeared on the homepage. Or maybe a non-answer slipped through the cracks several years ago and its appearance on the homepage now gives us the opportunity to expunge it, thus enabling us to better maintain the quality of existing posts.
Despite the above factors, it can be unpleasant for someone to visit the site and be greeted with 10 old questions on a specific topic. What I have seen on other Stack Exchange sites, and have done myself here on a few occasions, is spreading out the edits over a period of time. If you want to create a new tag and add it to 15 existing questions, you can do it over the course of a few days. Perhaps edit only one or two questions every few hours so that the homepage never becomes overloaded with bumped questions.