How can we handle data at multiple levels? ()

I have a "Package" module where I can configure various different kinds of packages(global level). I have also extended the "res.partner" object to have a many2many relationship with "Package" module as various packages can be assigned to partners(customer level). Now, I want to be able to configure packages on customer level, in other words, I can select a few packages from the many2many list and edit a few fields, but I want those changes just to apply for the current partner and not the (global) package itself (current behaviour). Essentially, each partner can have customised packages on a base "template".