Cells formatted as currency changing to custom on reopen when user changes currency symbol

I have designed a spreadsheet that people in other countries will be using. All the currency cells are formatted as currency, so for me the $ symbol shows. When I go into my control panel and change the default currency to Euros or something, then all the cells formatted as currency change to the Euro symbol, which is perfect. However, when I close out of the workbook and then reopen it, it no longer shows the Euro symbol. It shows the American dollar because all of the cells formatted as currency got switched to custom ("$"#,##0.00), so it doesn't read the computer's default currency setting and instead forces the $ symbol since it is a custom setting.

When I change my control panel back to the American dollar, the cells are once more formatted as currency, not that custom setting.

I had a gal in another country test it, and same thing. She can't get the pound symbol at all. Since her computer settings are already configured to the pound symbol, when she opens the workbook for the first time, all of the currency cells are custom cells forcing the $.

This is a problem since my workbook will be used from people in a variety of countries. (No need to do any conversions as the user will be entering in the amount. I just need the symbol to change).

How do I get these cells to STAY as currency ones, so it reads the computer's default currency.

Or is there some VBA where a user can enter in their symbol and every single cell marked as custom will change to that symbol? Since their workbooks are showing custom for any cell I had made currency. OR some VBA, that will make it so they don't switch to custom upon opening.