At some point, the UDID is being processed by code, so you don't really need to permanently modify anything: you just edit the code that generates it and make that return something different. These kinds of changes are very simple using Substrate, the library we all use (that I developed) for changing code at runtime. For the UDID, the obvious candidates are "edit every app so [UIDrvice uniqueIdentifier] returns fake" and "edit lockdownd so it calculates the wrong value every time it is generated".