BuddyPress.org

Download this plugin and check out the code: https://wordpress.org/extend/plugins/custom-profile-filters-for-buddypress/ It will show you the basic method I used to modify specific xprofile fields. Short version: you can filter the output of xprofile fields in general, and then you use a conditional to detect the name of the profile field that you want. Not enormously elegant, but hopefully that code will get you part of the way there.