custom wordpress plugin

i have paid plugin work on wordpress script "member system" and it's very good for me i don't need and more features . this is the plugin [login to view URL] i want custom this plugin to work on many website with one database like "openID" for EX: i have web sites "a","b","c","d" and the main website "one" - if visitor sign up for example on site "c" with username "jo" then the "c" website admin can edit "jo" details + "one" , but site "a","b","d" can't do that - "jo" can sign in on all these sites with same information and no need to re sign up again . - if other visitor sign up on "a" site with username "boss" the he can access to all these sites with same username and he can edit profile and personal information on all these site . as general : - any website admin (a) can edit the users register on (a) site only and can't edit users register on other sites like (b)(c)(d) - site (one) can edit and delete (full access) on all users on all sites - user can edit his profile from any these website and the database update instantly on master db (one) and site he sign up on it i need this plug in work with secret code so every website must have uniqueID with unique Secret code . if you need more details please let me know