I think it has more to do with a conscious decision to follow a set of beliefs.... a way of life if you will.... more than being born someplace with a set of genomes or genes.
Being born somwhere can make you a citizen or member of a culture, but that doesnt make you a "true believer"... a blind follower...
We are a compilation of our experiences... both learned first hand and through a secondary means like books or word of mouth... but we are not guaranteed to be what others before us were.
You choose a religion, you choose a hair style, you choose your own lifestyle.... but you choose these things of your own free will. Not because it is all you know or have experienced or have been "programmed" to believe to be normal.
My parents were both "flower children".... but I am no hippy myself.
The belief or feeling of belonging... being a part of something bigger than yourself... that can be a huge influence on choices and decisions.
What you choose today will not always be what you will choose tomorrow.
The clones trained by Mandalorians became Mandos, Corellians gained Correllian beliefs, and so on. But these were learned beliefs formed in a very closed society. Not much choice there.
And how many clones exactly did they say chose to leave or go awol or whatever you want to call it? Less than one percent... millions of clones and they chose to stay with what they knew.
But once given a taste of freedom and a few choices and being allowed to make their own decisions, the result was drasticly different although they chose to stay together.
It is a choice to live a certain way... a following of beliefs... Not genetics or place of birth.
Boba Fett is Mandalorian by upbringing and belief, If not by action. Not a communal person, selfish and self centered, I before all else. Not a truly Mandalorian way of thinking or behaving. But then Jango was not your archtypical Mandalorian either. A loner (Boba)was raised by a loner Jango). Both chose to be Mandalore when confronted with a crisis, to benefit their culture and ensure the survival of their culture.
If that does not make them Mandalorian, then nothing does. And they were both Mandalorian when it could be a death sentence to be so.... I guess that helped them become the efficient killers they were and to achieve and maintain the level fear their names would result in.
End of rant... for now.