The guidelines are definitely somewhat malleable, so long as one follows the explicit words.

The actual language in the rules only specifies the required visible when marking someone as a criminal, and then informing them of why they were warranted. People tend to be lazy on this. People who are lazy on this do miss out chances for upward mobility, or at least get it delayed.

There isn't any other requirement to be visible while on duty that I'm aware of, so there is nothing negative towards anyone who hangs around hidden/invis/duo and then warrants people. It's more appealing when someone takes that and RP's it out - that is to say, understands the value of visibility in deterring crime, but maybe has a focus instead of drawing out criminals, catching, and killing them.

If you're talking about the additional books in the library, remember that some are rules/required, and some are simply guides/tips. The latter don't have to be followed.