Rule #1: There are no rules.
There are guidelines. Traditional ways of writing. Requirements for certain forms of publishing or publishing houses.
As a writer, you need to be aware of what’s expected, especially if you want to be published by a specific publisher (or publishers) or in a particular form (electronic or paper).
Rule #2: Rules can be broken
For every rule you’ve heard or learned, someone will come along and break that rule.
If an editor can read and understand the story, if it can be published using the publishing tools available, and if readers buy and enjoy the story, it doesn’t matter if the writer didn’t follow the Chicago Manual of Style, or if point-of-view changes from paragraph-to-paragraph/page-to-page, or if you jump from first person to third.
BUT, if you are going to break the “rules”, you must understand what you are doing and the reader must be able to read and understand the story or article. You must also realize that breaking the rules may make it more difficult for you to be traditionally published.
That said, you are the writer. Change comes from breaking rules.
Rule #3: Don’t get hung up on rules.
It’s the story/article/poem/memoir/opinion piece that’s important. Grammar, punctuation, formatting can all be changed once you have your ideas on paper (or in a computer file). It’s what you write that’s important. How you write it (punctuate it, format it, or spell it) can always be corrected (if needed). Focus your energy on the content.