What You Are In The Dark: Teir (honor, in the Eldraeic sense) and the Code of Alphas are very, very clear on this point. Honor is not face or reputation; they are not honor. They are nice rewards for it, but you should throw them away unquestioningly if the necessity to choose between them comes up. It doesn’t matter if no-one else will know; you can never escape knowing, and by knowing, being. (And even if you redact your memory afterwards, you’ll always know that there’s something you couldn’t know.)
Sacred Hospitality: Absolutely. And even more so once spacer culture arose, because if hospitality was sacred when it was merely cold and hunger that would kill you, it’s even more so when you consider the very large number of ways in which space can kill you, given half a chance. Or not-quite-terraformed worlds, for that matter.
The Code of Alphas, in that subset called the Code of the Hearth, lays out the rules for hospitality pretty clearly, and they’re refined in the Common Social Protocol and such later elaborations as Madame Allatrian’s Garden of Exquisitely Correct Etiquette. It’s got symbols, rituals for entry (not bread and salt; asking for hospitality from the hearthmistress of the home and receiving it – an enhanced form of the ironclad custom of proclamation in which one must announce oneself on entering anyone’s property , or be deemed a trespasser) and departure and even formal disinvitation, customary lengths, customary expectations both simple and reciprocal, and so on and so forth. Providing it isn’t strictly an ethical obligation, but it is a moral one and an ironclad custom, so turning someone away who isn’t more than simply an enemy  without a good reason may well have unpleasant social consequences.
Even inns and hotels, which are commercial operations, fundamentally base much of their operation around the expectations and customs of hospitality.
 And, yes, that does not just mean people’s homes. There ain’t no such thing as a “public accomodation” in Imperial law or custom. When you go into a shop, you introduce yourself to the proprietor, or (in larger stores) their representative or even their automation. Otherwise you are trespassing and subject to all the consequences at the property owner’s discretion; and while those are unlikely to be severe, at the very least, you are being extremely rude.
 You’re supposed to offer hospitality to honorable enemies. No-one wants to gain a cheap and cowardly victory by letting their enemies starve or bleed to death, belike. On the other hand, you aren’t obliged to take dishonorable enemies into your home – but even someone invoking this clause may well pitch a tank of oxygen out the airlock, for civility’s sake.
Obstructive Code of Conduct: The Imperials would certainly argue that the Fundamental Contract, with its insistence on protecting people’s life, liberty, property, and contracts would be one of these. (Of course, some non-Imperials would point out that, given the very large number of societies in the Galaxy that aren’t nearly so fond of those, the Contract also lets people like the Sanguinary Enforcers of the Liberty Ethic set the war-drums to beating any time they feel like it; which is unfair, but not completely unfair).
Also to be mentioned here are the Code of Alphas (the rather detailed Eldraeic honor-code with specific sub-codes for each daressëf), the Five Noble Precepts (entropy is bad, and here’s how not to feed it), and, for military purposes, the Ley Accords (the basic rules of “civilized” warfare – although since they’re mostly reciprocal rules, anyone who prefers uncivilized warfare will find their challenge happily taken up. Less happily for them, usually.)