Wanted to establish this thread for more detailed discussion of this fragment.
In his Problems, Epicurus asks himself if a Sage, knowing they will not be caught, will do anything the law forbids?
First of all, it is likely Plutarch is being typically unfair here, as i imagine right after this Epicurus may have mentioned examples like helping a friend, or acquiring food in need. But Plutarch uses this to suggest unfairly Epicurus would be okay with things like murder or sexual assault. Notice how Plutarch conveniently doesn't mention what the "anything the law forbids" actually is.
For my part, i believe the proper interpretation of this can be as follows and requires a careful reading of PD35, which is related.
It is impossible to be confident that you will escape detection when secretly doing something contrary to an agreement to not harm one another or be harmed, even if currently you do so countless times; for until your death you will be uncertain that you have escaped detection. (Peter Saint Andre translation)
In this Principal Doctrine, Epicurus seems to specify that is it the agreement to neither harm each other which is genuinely impossible to have confidence in escaping. However, despite Hicks translation that "It is impossible for the man who secretly violates any article of the social compact to feel confident that he will remain undiscovered," The Greek itself to indicates the "neither harm nor be harmed" being specified, so things like murder, sexual assault, terrorism, and theft done in a way which genuinely threatens or harms someone else, such as stealing their entire life's savings or hostage taking for extortion, but not just any part of the law preventing confidence in escaping.
I think it follows that Epicurus thinks there may be instances where the Sage breaking the law may be "hard to determine" for Epicurus, obvious cases being helping a friend, escaping a country if one needs to, or getting food without better options, along with other more minor things such as gambling, piracy, speeding, taxation loopholes, or other things, if unenforced or secrecy is assured, while i still believe he would generally advise against heavy use in such things for their anxiety. He considers these more "hard to determine" unlike examples of harming another person, which the Sage would say "absolutely not". It is these things which is the part of "living justly" as per Principle Doctrine 5
In short, while strictly rejecting anything which genuinely harms another as preventing serenity of the mind permanently because the nature of "harming one another" always creates fear of discovery, heavy punishment, and resentment, but other things without this nature which don't produce the same anxiety or risk, are more "hard to determine" and context dependent but generally discouraged.