I have finally found an answer. With methods described in the links above one can only override “client api”. Admin panel uses completely different set of api which cannot be extended this way and the documentation is not explicit about that: Controller update method is not called from the admin panel · Issue #18214 · strapi/strapi · GitHub
So my question now changes to: How to override “strapi admin api”? I have a relation between two entities and on the edit screen I want to filter out certain values (in other words there is some business constraint telling which entities can be linked together and I do not want to display entries which are not allowed).