variable to control currency(format&conversion)

hello!

I'm about to revamp this UK based companies excel sheets, make them make sense and they continually switch between USD and Pounds.

I would like to do something like Choose() and change all the appropriate currency formatted cells from USD to Pound, or Pound to USD. and I would like it to convert between the two based on the exchange rate (another variable I set).

Ideas? Is this possible without doing VBA?

Thanks!