Changing transform_null_equals (and other settings)

Hello all,

Is there a way (via a sql cmd) to change the "default" value for this settings?

So - just to be clear.  I understand that if I send the following command:

   "set transform_null_equals to on;"

I can set it for a given connection.  However, I guess what I really want to know, is there a way to literally (or
effectively)change the value in the Postgresql.conf file via a sql cmd?  Or do I physically have to edit the value in
thatfile (via a text editor or pgAdmin III, etc) 

I hope my question makes sense.

Thanks in advance and cheers!

David