Change the 'comma style' button function

Using Excel 2003 I am trying to change the default style of the comma button to format negative figures with brackets, ie. (50,241,992.00)

I have managed to do this by formatting the cell using the current setting style for this button:-

1. format cells
2. Format -> style -> modify
3. In category -> custom, then entering the following

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This does apply the settings I want, however when I start a new book I do not have the settings I had just changed.....

I:confused there a way to apply the setting to all the books new and old ?