number_to_currency() in the view?

On p. 93, AWDWR(3rd) it says,

Well rather than having format strings spread all over the place, you
centralized the concept of formatting a number in one place, the
number_to_currency method. If you wanted to change currency formatting
you'd just have to change that one helper.


How do you override a helper method?

Same as any other method ? (although I suppose helper :all might throw
a slight spanner in the works)