I feel most of what you are asking, is already in fact part of the racing etiquette. It's not a rule or regulation per say, but it is what is generally accepted to be fair.
In the Baku topic of this year in the aftermath of the clash between Max and Ricciardo, I posted this very enlightening video:
In it, they explain the difference between defending and blocking. In other words, it's blocking, when the driver ahead reacts to the movement of his attacker. It's akin to using your car as a moveable blocking object. Obviously, in todays racing with DRS, the speed differentials between a car attempting an overtake and one defending can mean closing speeds of up to 10 meters per second. The wheel base of a modern F1 car is <4 meters. At such closing speeds, obviously, there's a certain reaction time one needs to account for, the closing speed one travels in that time and the ability to still safely maneuver the car at speeds above 300kmh. You also need to account for loss of downforce when driving in another cars wake.
Obviously, when the car in front jinxes into your path 10meters in front of you, there's pretty much nothing you can do to still avoid a collision. In that sense, the etiquette is and should be that drivers defending their position should cover the inside early enough to it not be deemed a blocking maneuver (e.g. as a reaction of the car behind). If you go to the inside before the car behind you attempts an overtake, it's fair game.
Now, putting this into practice isn't that easy. Sometimes, drivers, especially the ones overtaking, will move late as a result of using the tow and slipstream for as long as possible. The defending driver can not possibly know if he will then pull out to the inside or outside. Sometimes, it goes wrong, sometimes it doesn't. Still with such high closing speeds, I feel it's the job of the defending car to take that into account by making their intentions clear well before the braking zone that they are covering the inside and that the inside is a "blocked path". By the rule that only 1 defensive move is allowed, this forces the defending car to stay on the inside. If he moves back to the racing line to take the corner, he must leave at least a full-car-width of space to not crowd the other car beyond the track.
Not for nothing, Rosberg's Championship is the only thing that lends credibility to Hamilton's recent success. Otherwise, he'd just be the guy who's had the best car. — bhall II