Note Custom formats are saved with the workbook. To have Microsoft Excel always use a specific currency symbol, change the currency symbol selected in Regional Settings in Control Panel before you start Excel.
If you want to save a new style to the button, you need to create a macro that applies the style and save it to your personal macro workbook. Then assign the macro to the button. As long as you're on your PC, you it should be there at the application level as opposed to the file level.