John,
You will still pay catalog price...from the year you ordered. You can expect a $30.00 fee for the order change. Orders can be changed, but it is limited. For instance: You cannot change from a #24 to a #12-11 "Smithsonian". In your particular case there is no problem with the changes you want to implement.
Please make sure you send your handle material, sized to the proper dimensions for the "new" order. Hope this helps...
Best, Capt. Chris