Create fields for the information for an alternate footer and show the field group on every page. Wherever you are displaying the footer check for this alternate information and display it instead of the default.
I usually create options pages where the client enters footer info. When I want to do something like this I then create a field group for pages. I usually put a true/false field at the top for “Create Alternate Footer”. Then all of the rest of the fields are conditional based on this field. In my template I check to see if that field is true and then show the right footer.
