I want control over the order in which roles' columns are displayed on the Permissions page..
I want to add code to my module installation file so that, after newly-configured roles' yaml settings have been applied (they list the permissions for each new role), it displays all the roles in the order I want.
How do I do this?
The roles' yaml settings are part of a module created by Features. Enabling the module in the target Drupal 8 system adds the new roles in the wrong order.
It is not possible to include the weights of the anonymous; authenticated and Administrator roles in the feature / module's yaml files as this causes a conflict that prevents the module from being enabled. So the solution is to apply the weights programmatically.
 I mistakenly thought that the order of the roles' columns related to an hierarchy / inheritance of permissions. Corrected by @Berdir, thanks. Nevertheless I still want to display the roles' columns in the way I choose, so I have edited this question to reflect this.