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I assume you are creating the Focus file via HOLD FORMAT FOCUS -- which will indeed replace the .mas file along with the .foc file -- and you have added information into the .mas file (joins, defines, titles, whatever) that you wish to preserve across such refreshes.
You can either  save the enhanced .mas under another name (an "alternate master file") , and use USE to point to the focus file [ that's essentially WAZ's second approach ]; or,  create a Business View synonym that points to the HOLD file.
The former operates without looking at the .mas that the HOLD refreshes, and so will likely break if you make any change to your TABLE HOLD request. The latter operates through the underlying file's .mas, so it can survive some such changes.
Either solution is keeps all the filenames distinct, as opposed to Tony's suggestion.
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