Duplicate the track. Then change the media. This should keep keyframes for track-related effects but if you want to keep the keyframes for events, you'll have to use a trick as suggested above. Close the project, rename the media, open the project again, specify new media when prompted because of the missing file.
I've done the "duplicate track" part but haven't tried the close project, rename media, etc part although I use that trick quite a bit in other contexts.