I'd like to change the mailtpl file for a list. I'm testing on a sample
list. Before I do any changes, I'd like to find out how to back out of the
changes if they don't work.

If I update the list mailtpl file by sending a message to listserv with the
first line  

PUT listname MAILTPL PW=XXXXXXXX 

and put the part of the mailtpl file I want to change below that and send it
to listserv that should update the mail.tpl file. 

If I find it didn't work right and I want the list to revert to using the
default mailtpl file how can I do that without sending a duplicate copy of
the default mail.tpl file to the list? It seems like unnecessary duplication
to have the same mailtpl file as the default for all lists and for the
individual list.