Frames are pretty much your only means of reverting back to a previous change of a particular file when working in Windchill.
While not ideal, you could revert back to the previous frame that included the previous iteration of the part in question, open that part in Pro/E and do a File > Save As > Save a Backup to save the file to disk. Revert back to the latest frame and bring the saved iterations back into the workspace--either via File > Open in Creo or Tools > Import to Workspace in the workspace.