excel how to lock the format of the top cell

Users questions: excel how to lock the top in the format of the cell, but does not lock the content. For example, I will be the contents of cell A1 in this font lock is "bold, 20, bold," but that people can modify the contents inside. I ask how to set up?
Experts answer: cells selected, set the "bold, 20, Bold "and then enter the content of this format.
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