Remember, if you change your existing post too much some of the answers may become confusing if they address points that are no longer there or are stated differently. So don't edit your question just to remove a mistake — we all make them and others can learn from yours if you leave them up.
If you want to add a note to your question, you can draw a horizontal line and write "Edited to add: I now realize ...". But remember, this isn't a class where you have to demonstrate to your teacher that you have internalized the answer; do so only if it would be helpful to future readers. For instance, when I glance at your first linked question, there is one short answer that is top-voted and accepted. Future readers can read your question and that answer, and get a complete picture. They are unlikely to gain anything from you repeating the answer as an edit to your question, and sometimes edits like this can make the flow of ideas harder to follow. So I wouldn't bother there.
It takes a while to change from writing up math for homework to producing posts that best help future readers, so thank you for asking about this and being considerate of how others use the site.