Modify an OSSN Website. (PHP OOP Coding.)

Effectively, I need a component built for an OSSN (Open Source - Social Network) site. It needs to replace portions of the core, to function. I need to have leveled tiers, for content, and not make the higher leveled content tiers visible to the user, until they are of that tier. The site makes use of the Paid Access component, and needs to engage that component, as the very base level access to the site is free, and then the second / higher tiers are Paid-For content. The component needs to work with the system, and hopefully not modify the base php scripts for the kernel. (We want to be able to upgrade the website, as updates come out, and not lose the modifications.) The component needs to allow us to change the user's level, as well as track Current/Normal levels. We'd like to pop them down to the "free content" access if there's a problem with their subscription. The subscription is handled by the Paid Access component, which we already have. We just need a Level Access component. Areas affected: Users, Groups, Paid Access, and potentially a library feature to be added later.