First, set up a model cell with the replacement formatting. Next, press Ctrl+H to launch the Find and Replace dialog. There, define both the Find What and Replace With formatting by clicking "Choose ...
Click "Format" next to the Replace With field, and select the correct number format in the Number tab (in this case, ...
This guide describes how to grey out unused cells in Excel in Windows 11/10, apply a solid fill color, use Conditional Formatting, or hide unused rows/columns.