I'll quote myself again for reference:
The 'code' is more of some general guidelines. You'll find out more about what is considered orthodox and unorthodox when you begin the first chapter: but in essence, orthodoxy is what the main orthodox sects say it is. But yes, generally an orthodox person is seen as an forthright, noble, upstanding guy, while unorthodox characters are deceptive, cunning and sneaky. This can be reflected in the techniques they use. The scale will affect your reputation with the various sects depending on which side they skew to.
You can also be hanging around with unorthodox people despite being upstanding yourself and get tarred with an unorthodox reputation, which may close some paths. Basically, it is impossible to please all factions.
The stigma associated with being unorthodox will be that you won't make any good first impressions on orthodox sects. Your behaviour will generally be too carefree and chaotic for them to respect. Of course, you might build personal friendships by bailing their asses out, but all in all they won't treat you nicely.
Orthodox sect members are also the majority in the pugilistic world, so by being unorthodox you will naturally become an outcast. Of course, there's a thriving underworld of bandits, assassins, mercenaries and all sorts of evil-doers, and these are by the pugilistic community's definition
very unorthodox, so you won't be
that lonely. But it's definitely a more dangerous place to be for a fourteen year old boy. People will think you have a death wish to willingly hang around with brigands and scoundrels.
As for techniques, unorthodox techniques are stereotyped as being cunning and vicious. They might not be unpredictable, but there will be elements in their moves that are frowned upon by the more upright members of society. For example, they could be designed specifically to maim or mutilate, or they could involve the use of poisons and sneak attacks using hidden projectiles. There are also the skills that harm the user when practiced and skills that have a high chance of driving the practitioner into insanity, or even changing his or her personality for the worse (this includes self-castration). These are techniques that can only be used in a deathmatch, as they are highly lethal. Orthodox techniques are healthier and safer, and in terms of power both types are ultimately evenly matched, though unorthodox techniques may increase your power faster than orthodox ones do, and usually at a price.
Murder, by the way, is heavily frowned upon by the orthodox sects. They do fight to contest their strength and gain supremacy, but in non-lethal sparring matches. Of course, killing is allowed in vengeance - say, someone murdered your family and you have rather definite proof - and also allowed in self-defense. This is not to mean that the unorthodox are totally chaotic with no rules; there are several major organizations that keep a semblance of order, though in general it is like herding cats with them.
Xu Jing is able to learn both sides of martial arts due to his high stats. The only arts he can't pick up are those that rely on the user being retarded enough to truly comprehend the essence of the technique.