Conventions and penal codes define useful standards.
A convention is some rule, or set of rules, which is formulated by one person, to be used not only by himself, but also by other people: It is, of course, their free decision to sign or not to sign this convention. The main advantage of signing it, in comparison with formulating an own similar text, is that a convention usually contains obligations relative to other signers of the convention. Thus, if you sign it, it is not only you who accepts some restrictions relative to others, but automatically the other signers accept the same restrictions relative to you.
The convention gives only two possibilities: To sign or not to sign.
A standard which gives more freedom of choice is what we call penal code: The penal code also fixes the content - the text of the articles of the code, but does not fix the penalties for violating the given article. Those who accept a given penal code are free to define these penalties.
In particular, they can set the penalty for some article to zero, which means that for them it is not forbidden to violate the given article.
Therefore, a penal code appears to be a useful way to unify lot's of different conventions in a single place. Those who would sign a particular convention accept some penalty for violating it, those who don't like to sign it assign the zero penalty to it.
Using standards has lots of advantages:
For example, you want to find people for a job. Then you can define some minimal standards for rules: Some set of conventions they have to sign, and some minimal penalties they have to accept for various things. These data you can give to a robot, who can do the job of finding those who fulfill these requirements.
The possibility of using software for evaluating the rules of others in a fast way is a decisive advantage of using standardization. But it should be noted that such standards appear also without this necessity, and also in situations where the state has no influence at all. A particular example are the GNU standards for software licenses.
There is no and cannot be any central instance which defines the conventions and penal codes. Everybody is free to propose some convention or code. People decide which of the conventions they prefer. Of course, one of the values of conventions is that other people use them too. Therefore, it is likely that there will be not too much competition, but only a small number of competing conventions for every particular question.
Who will be interested to develop conventions and penal codes? Today, these are politicians - people with a strong interest to control the behaviour of others. An especially powerful group of them are motivated by their religious beliefs: They would like to force others to follow the moral code of their preferred religion.
Now, we can expect that those motivated by similar motives may participate in developing conventions and penal codes too. But they are much less likely to do this, because it doesn't allow them to reach their aims: Whatever their proposals, nobody is obliged to accept them. In particular, religious fanatics will not reach much: Those who don't share the particular religious beliefs will ignore the corresponding proposals.
A typical property of democratic laws is that they are the results of compromise: Without making compromises, it is usually impossible in a democratic state to make some proposal a law. What democratic lawmakers tend to think about are therefore questions like "which part of the law is more important for me, which parts are less important". This is even more complicated by the problems of democratic decision making, where a particular politician is often evaluated by his ability to win elections, and where the public interest is focussed on a few central points in the political confrontation but cares much less on lot's of other points. As a consequence, democratic law is usually bad law: It's nature as a compromise makes it inconsistent, and inconsistence of law means injustice. Of course, consistence alone does not give justice. Nonetheless, really good and just laws have to be internally consistent, and are therefore unlikely to appear in democratic states.
Instead, those who develop conventions and penal codes recognize that they have no power to enforce them. All they can do to improve the chances of their proposals is to improve their quality. Therefore they are unlikely to make political compromises which lead to inconsistencies. Thus, the result will be much more internally consistent conventions than imaginable as a political compromise.
Internal consistency is a prerequisite for real justice. On the other hand, there will be also lot's of internally consistent but unjust proposals. And unjust proposals become even more radical, dangerous and unjust when they are made consistent. Is this dangerous? Probably. But it is much less dangerous than the same radical proposal as a democratic law, where everybody is forced to follow it.
There is a reasonable hope that the conventions which will win will be much better than laws which win in a democratic process. An important point is that, different from democratic lawmaking, your own decision matters for you. If you cry "Sieg heil" in some Sportpalast or not does not influence anything. Your single vote in a democratic election does not change anything except your personal feelings. But the rules you accept in the network change a lot in your life. So you will think twice before accepting radical rules: It's only you who has to follow them.
It is very difficult to change conventions. In some technical sense, it is even impossible: Once a convention has been proposed, and at least one other person has accepted this convention, the convention cannot be changed anymore without the agreement of the signer. Even more, if somebody else has made a contract with the signer, relying on his signing the convention, the convention is implicit part of that contract, thus, the signer may need the agreement of all those who have made contracts with him as well.
Nonetheless, there are reasonable ways to improve conventions. The way how to do it is to introduce new versions of the convention distinguished, as usual for programs, by a version number. On the site where the convention is presented, it is the newest, best version of the convention which is propagated. The typical user who is not interested very much in the details of the convention will be informed about a new version and can, then, sign also the actual version of the convention quasi automatically. Then, a robot may check if some of the contracts he has made before depend on earlier versions of the convention. If they do, the robot can propose a modification of the contract and forward this proposal to the other signers of the contract. If they agree, everything will be based on the new convention, and the old convention may be removed from the list of rules. If not, the old version of the convention remains implicit part of existing contracts, but may be removed from the list of rules which are obligatory for him in general.
Thus, changing aconvention is a process which may take some time. And it may happen that the old version survives many years.