[Wade Francom]

I believe the process would be to create a duplicate timeline…this time with the video settings to match your original HD video. Then you select everything on your editing timeline and paste it to the new HD timeline. Of course, by doing this, Final Cut is going to want to render those files to the HD settings you have on the new timeline. Rather than do that, import your HD files, select everything on your new timeline, then go to “Reconnect Media” (under the File tab), select online files, and then browse for and select the HD files. This should replace the old files with the HD files on your HD timeline, and therefore skipping any need for searching or re-rendering.

I believe that’s how it works.