I'm a little confused, also. I know that my BLI Santa Fe northern has an operating pilot coupler, so are you talking about the newer Bachmann Santa Fe Northern? If so, I think that the non-operating knuckle coupler should be a separate casting, easily removable from in back of the pilot mounting with a small X-acto blade and replaceable with an operating Kadee long-shank coupler and box. BLW for me means "Baldwin Locomotive Works" which produced all of the prototype Santa Fe 4-8-4's--it doesn't mean much about the MODEL locomotive manufacturer.
Or do you perhaps have a brass locomotive? If so, the coupler should be held on by a tiny screw or pin under the pilot. Simply remove the pin or screw, the coupler will drop right off, and then again, using a drill and tap, you can replace it with a long-shank Kadee.
The reason I say 'long-shank' is because no matter WHO the model manufacturer is, the Santa Fe 'boiler tube' cow-catchers extended quite a ways out. You need a long-shank coupler for the trip-pin to clear the point of the pilot.
Hope this helps.
Tom 