One can invent anything one wants, but the reality is that a policy is not binding. It just isn’t. One might be criticized for going against a policy, as the two parties have criticized each other for violating policy by such devices as the “nuclear option”. But they’re free to do it. Mueller is nothing if not an adversary of Trump in the investigation. It was, after all, Trump who was being investigated, and not willingly.
And apparently, the policy didn’t exist during the Watergate mess, because it appears Nixon was, indeed, indicted, as I cited before. But no matter what, it would be an absolute dereliction of duty on mueller’s part to draw back from seeking a criminal indictment if thought he had the evidence of it, all because of policy to which he was not a party and to which he was not bound. I’m not sure whether the crime “misprision of felony” would apply to such a dereliction of duty, but it might.
Mueller didn’t have the evidence, and, as many have pointed out in these threads, he turned it over to congress for a political resolution, and as a political matter, (which it always was, in truth) not a criminal matter. In doing so, he rolled the dice. He’ll get an impeachment in the House if a majority of Dems think that would help them politically, but a conviction in the Senate is extremely doubtful.
The Dems should be angry with Mueller, and probably are. To avoid having a crashing and embarrassing failure as his “swan song” in law enforcement, he handed it to them. They are now almost forced to start an impeachment because if they don’t they’ll have a hard time excusing that failure.