Changing the symbol for all currency formatted values in a spreadsheet - how?

I've just stumbled upon this thread as I attempt to solve a similar problem.

Is there a way of identifying just those cells that are already formatted as currency (of whatever symbol) and then apply a new symbol or preferably a three letter international currency code? I have coded something using ranges but as the currency cells are dotted around the sheet it's impractical to code in every cell reference. I was looking for something that looked for cells already formatted as currency then changed the symbol or abbreviation with the one from a selection list that the user can select. That way it would leave any non-currency formatted cells untouched. I have applied the code to cell ranges but in the sheets I am working with there are cells that aren't easily referenced in a range. I tried doing it in a real sheet and the coding too me longer than manually changing the formats. The way I coded it feels wrong to me but then I am very new to this

I think the attached should illustrate what I'm trying to achieve. The test would be once the code is in place, I could add a number, format it as currency and then make a different currency selection in cell A1 that would change all currency cells including the new one, to the chosen currency.

Thanks

Or are you suggesting that I create a set of styles
GBP Style
USD Style
EUR Style

etc and then have some sort of picker to select the appropriate style that would then change all the cells where the currency style applies?