Modify Existing Wordpress Plugin To Add Functionality

We currently have a wordpress plugin (1 PHP file) that when passed a certain URL with special variables appended to it (matching criteria), redirects the user to a special page. (e.g. [login to view URL]) Right now it will redirect to a pre-set page. We need the plugin modified so that it can send to different URL's based on the variable. Something along the lines of [login to view URL] , link2, link3 would be fine, with being able to pre-set the links in the plugin configuration options.