A lot of people "customize" their trailers after bringing them home...even the new ones! Some friends of ours totally removed the "sofa" in their Airstream to replace it with two lazy boys which they love.
If you are at all handy, you can remove the bench (or a portion of it) yourself to add two swivel rockers as you suggest - or there are pros out there that can to do it for you. No problem. I know there are some folks that were at Alumapalooza last year (at the factory) that do custom Airstream modifications in the exact same finishes as modern rigs - they are pretty pricey though, so I didn't pay much attention. Besides, we do all our own work on our vintage trailer. Regardless, the interior of these things go together pretty easy (even the new ones) - basic tools like a screw gun are all you need. You may have to make some kind of "end panel" at the new end of the shortened bench, but that could be pretty simple too.
If you
do decide to modify it - try to think of your trailer's "next owner" who may want to put things back the way they were...they will appreciate it if you save the parts removed.
Good luck in what ever you chose to do!
Shari