Changing the Preferences Configuration file

[Nick McCulloch]

Hi,

I have created a custom Tax invoice and it appears correctly under 
Reports -> Business and works perfectly fine.

What I would like to know is how to do is change the option under Edit 
-> Preferences -> Business -> Invoices -> Report for Printing
I would like my new custom Tax invoice to appear in this list so it is 
my default for any time I print an invoice rather than having to open 
the invoice then select the new custom invoice and the invoice number.

Which configuration files can I change so that my custom Tax Invoice can 
be selected and be the default for all printing of invoices.

Thanks

Nick