My understanding is that the rule can be used in court to strike down actions in court. I was wondering whether it might also perhaps be used legitimately by someone, outside of a court case, and apart from a court ruling, to determine that an action that would otherwise be considered illegal, was in fact lawful, in a legal positivistic sense, by virtue of this rule.

For example, perhaps it's the case that photocopying a page of a book, in a particular situation, would be considered to be a copyright crime without the use of the rule. Is it then the case that the rule might be able to be invoked, to say that the photocopying is perfectly lawful? Or is it perhaps alternatively the case that the "de minimis non curat lex" rule throws no comment on the legality of the photocopying, and that the rule can only be used to determine unenforceability in a court of law?