Not really, since upstream will have as much trouble requesting the modifications, or even knowing about them, won't they ? :)))
Nothing says it should be an individual request, or time-limited, or anything. I'm not sure whether such requests would be kindly regarded in court but danger UX-lawyerbomb. (first appeared in http://lists.debian.org/debian-legal/2004/07/msg00179.html repeating for benefit of BTS)
-- MJR/slef My Opinion Only and not of any group I know http://www.ttllp.co.uk/ for creative copyleft computing "Matthew Garrett is quite the good sort of fellow, despite what my liver is sure to say about him in [...] 40 years" -- branden