Not sure what kind of modifying language to use?  Use an addendum to try to do the work for you. They are designed to be convenient and to take guess work out of modifying publishing agreements. They are intended to seek the kinds of rights that most academic authors would value.  There are several different addenda to choose from, and the Office and Scholarly Communication can discuss which one might be best for you.

One of the most widely used addenda is from SPARC (the Scholarly Publishing and Academic Resources Coalition); “The Author Addendum is a free resource developed by SPARC in partnership with Creative Commons and Science Commons, established non-profit organizations that offer a range of copyright options for many different creative endeavors.”

Examples of other addenda include the Big Ten Academic Alliance Authors Addendum, the University of Michigan Authors Addenda, and the Science Commons--Scholar's Copyright Addendum Engine--which allows users to generate your a PDF that you can attach to your publishing agreement.