Say you have a small clan of badged yukkuri, like, about 10 or so
The type of badge is not important, for what is worth even a bottle cap is ok, as long as they consider the badge something to be proud of (like how graded yukkuri get one after working hard)
Now, let the yukkuri live their life like nothing is afoot
It could be in a controlled "wild" environment or you could feed and help them, but what matters is that they should make bonds and start making families
Now wait for them to make babies, if it's a stalk pregnancy it's better
When everyone is asleep, place a badge on each baby yukkuri (if it was a mammalian pregancy you have to wait for them to be born), and wait until these baby yukkuri become adults
By then, the parents probably made another litter, because little ones are easy
If you're fine with that, place badges on them too, otherwise try to dispose of the new babies as quietly as possible
When the new generation is old enough, have them make babies, and place badges on their babies too
After some generations have passed (assuming they didn't self-destruct), the yukkuri should consider these badges as something that "grow on their own"
Have a couple more generation pass, then, when distributing badges to the new babies, skip a few families
Since these babies never "grew" a badge on their accessory, they will be considered uneasy and probably die
Those families most definitely will be making new babies, but this time give them badges
The next time, select different families. but don't do this too often, wait a generation or so between each "miss", to avoid alarming the yukkuri
After some time, slowly increase the frequency to which unbadged yukkuri appear
If you want, you can even have badged and unbadged babies in the same family, what matters is that the yukkuri have to be scared of this "uneasy syndrome"
Keep an upper limit of unbadged yukkuri though, as they need to be an uneasy minority
As time passes, each generation will grow with an innate fear of unbadged accessories, so much so that they will try their best to have "easy" children
And so, at some point, yukkuri will give birth to babies whose accessory already have a badge
Do you think this could ever happen?