If your originals are Avid media files, and your transcoded files are Avid Mediafiles, and both versions are reachable (currently available in the Avid MediaFiles folders),
you should be able to relink to a specific resolution or 'any HD yadda'
You may need to do a 'load media databases' first, worst case you need to trash the media databases in the MXF folders.
Linking to AMA can be painfull, but linking originals to transcodes and vice versa should work fine.
Bouke
http://www.videotoolshed.com/
smart tools for video pros