A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Excel for Mac has no built-in features to Find/Replace based on formatting. It may be possible to write a VBA procedure for that purpose, but I can't speak to that capability.
It may not be helpful for the current situation, but for future reference: If you format cells using Cell Styles you later can modify the Style as you wish. Any cells which have that Style applied will automatically update accordingly based on the new definition of the Style. Please see the support article:
Apply, create, or remove a cell style in Excel 2016 for Mac - Excel for ...
The use of Cell Styles also is more efficient & more consistent than relying on direct formatting.