Alright, thanks to a good friend who suffer from insomnia we figure out where to find the right hook 
Here is it, it also adjust the form visuals and allow to select a minimum trust level from which the access to editing category will be available anyway (default trust level 0 to be in line with default discourse settings)
I’ll go create a new topic in the plugin section now.
Thanks a LOT @Canapin for pointing us in the right direction at the start 