The simplest approach would be to store the currency symbol in its own text field and don't select a currency symbol in number format.. Your layout would look like this:
and so forth.
If the fields are not to be edited, you can either use merge field to eliminate the space between the currency symbol and the number.
You also do not have to use a script to update the values. You could set up auto-entered calculations that automatically update the values when you enter a new currency exchange rate into the global field.
Amazing. Thanks :smileyvery-happy: Problem solved.