Thing is, we’re actually pretty flexible with this. If you cover the main aspects of your story in the open tags, and then add “additional tags at the beginning of the chapter”, you can still keep from acting as your own spoiler.
For example, you have a story which is het, set in an alternate universe, and an angst fest. So your main tags would be MF AU Angst. Then, you want to get into something which is a BIG trigger for most readers, such as rape, but it’s ONLY in part of a chapter. You tag in that chapter, at the top. It’s still an acceptable form of tagging, if your readers don’t like this particular content, they can skip the chapter and wait on the next one.