how do you swap key definitions?

[Steve Strassmann <STRAZ%MIT-OZ@MIT-MC.ARPA>]

I and several others are now using a DEC pro 350 (blechhh) running as
a vt100 to connect to OZ, but the keyboard has a particularly brain-damaged 
layout. How can I set up in an LOGIN.CMD (well, EMACS.VARS, I bet)
the magic which swaps back-quote and ESC. It would be nice to only do
this conditionally (as we DO use normal terminals occasionally), and
even better if this swapping could be done at exec for all of tops20,
instead of just babyl/emacs. Thanks,
-steve
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