First, I have no idea what the hell I’m doing in CatDV, although I can see it’s pretty awesome.
I was able to Export an FCPXML, import to CatDV, attach a new piece of media to the sequence, reexport as FCPXML and import that to FCPX in no time.
The sequence came in as 25p to FCPX
The media is not offline, but it’s all black meaning there’s nothing to play back.
Oddly, all info in FCPX points to the new/proper file (which would be your “finished” file, Chris).
More testing is needed. Sort of encouraged, though.