The contents are identical. Just change the extension on the file name in your file browser, or Open the .bak file in Designer (File > Open Workflow > Browse, then set to "All Files (*.*)" and select the ,bak file. Then Save As the yxmd.
You can rename it - just remove .bak and then it'll be useable again from whence it was saved. Not everything will be present since the time of creation/saving may have some differences.
