Back then Boeing would customize anything the customer wanted. You can tell ex TWA planes because all the switches are reversed. Down is on and up is off. On the overhead foward is off and backward is on. Stupidest thing I have ever heard of. We had one in our fleet. I hated flying that airplane.

But custom flap settings? I never heard of it and seeing that there is absolutely no obvious reason for it all I can do is scratch my head.