Hi Nicolas! Thanks for the compliment. Unfortunately I've never had to do this myself so can't give you an absolutely certain answer.

I've found a few resources that I can share which may help you out: This looks to be some really nice instructions on how to generally flash the system: opensourceforu.com/2017/06/beaglebone-black-flash…

This Forum post might get you going in the right direction. It's specific to buildroot: forum.beagleboard.org/t/how-to-flash-the-emmc-on-…