Automatically setting currency

I am setting up a template spreadsheet for tracking budgets. This will be used for budgets in both GB sterling and US dollars.

Rather than have to select the relevant cells and reassign the currency symbol each time I set up a new spreadsheet, is there a way in which I can use Conditional Formatting (or some other method) to automatically format the cells based on a reference cell at the top of the sheet in which I can just enter £ or $?