I am sure there are people who live by a code, but not a BDSM one.
Just because you spend the day in a chastity device, does not mean you have to identify as a BDSMer.
BDSM is a sub culture. Within it are different elements, maybe for example - MS or Ds... now those have more of a specific 'code' if you want to call it that - those being a dominant and a submissive in a power exchange of some sort or another. Some people live that. But even within those - there are unique paths.
If you really want to single out what makes a BDSMer think they live a BDSM lifestyle (a term I loathe) then it is the individualism is what singles it out - the one thing you dismissed slightly. Most people here have said it is an individual choice. If you want to know what makes BDSM - BDSM it is individualism.
But then, isn't that still present in other 'Lifestyles' too?
You cannot define an acronym, only the words that the acronym stand for.
Bondage/Discipline/Sado/Maso
Those are in an acronym, the definitions already.
Peace and Rapture