This is an odd question.
FCP will allow you to edit, fool around with, manipulate almost any video file. So, if you're asking if it's possible to re-edit a dvd-ripped movie... yes. It would be very time consuming, but possible.
Adobe Premiere is also a good program that would allow you to edit video, but I don't believe it's as versitle (sp?...sorry, i havent had any sleep) as FCP.
DVDSP doesnt allow the kind of editing that FCP does. Its simply DVD Authoring...but very good at it!
My problem, currently, is getting DVDSP to allow more than 90 mins of video onto a DVD-R. DVDSP1.5 only recognizes the .m2v file exports from FCP. .m2v files are DVD-Authorized MPEG2 video files. They are accompanied with either .aif files, or .ac3. Joining the two together gives you your audio and video for a DVD.
Anyway, hope that helps.