There are no rules except your ear. Basically, if it sounds right it is right and if it sounds wrong, it doesn’t matter what the book says, it’s WRONG. For instance, many arranging books and systems tell us to avoid the b9 interval but that can be one of the most colorful devices used properly. Many of the avoids of the arranging gospel are sometimes the most interesting. Check out Gil’s “Jelly Roll.” I’ve even used the major and minor third in a tonic chord with success. There are no rules except your ear.
However, if you’re just getting started you need rules to get you up to a level of understanding and competency. If you’re a beginning driver with a new car negotiating an unfamiliar road, you need all of those stop signs, caution lights, center lines or guard posts to get you to your destination. After you’ve done that for awhile, some of those driving aids aren’t as necessary and you don’t have to worry about the arranging police.