Re: The "Ten Commandments according to John"
As I have said before: there are ALWAYS exceptions, but in general terms people mustn't base their writing on them! Exceptions to the rule is what they are! And of course that is a pastiche of a Victorian novel, when the rules were certainly different.
Iain Banks sometimes swaps POV in a scene too, but he's a genius, and a bestselling novelist. When you have reached that position, you can play with things - as long as you are good enough to do so and they don't get in the way of the story. But for new writers, get the basics right.