How to customize Strapi backend (content-manager) controllers, services and validation?

For the Admin panel that would be our custom conditionals, which can only be customized in our enterprise edition. It is possible to do using extensions to the content-manager plugin but it’s a bit of a dirty solution that we want to get rid of in the v4 (at least the way it’s done right now, possibly replaced by a hook system).

The logic you are looking for is the conditionals system though: Configurations - Strapi Developer Documentation