Restrict category based security on portfolio level ?

Currently security on the portfolio can be driven by either portfolio level or category level. When permission is based on portfolio level - one can restrict users from editing data on portfolio level while giving them access to edit on Item level, while when the permission is based driven by category the user gets same permission on both item and portfolio level and there is no way to restrict them similar to portfolio level security.

So when the security is set by category is there a way to restrict editing data on portfolio level while giving user access to edit data on item level. (apart from writing any advance function on summary value of category).