Another kindof-tested idea.
1> Copy the model to new filename. (we'll no longer touch old model)
2> Open (new) model in MED, open the frame manager (under edit drop-menu)
3> Double-click the frame you want to keep. Click MOVE button.
4> Move this frame to BEFORE frame ZERO. (this makes it a new KEY frame?)
5> Still using Frame Manager, carefully delete all other frames.
(Its easy to accidentely delete the one frame you want in manager)

Save and done.