Each list has two names: short and long.  If no long one is
defined (* List-ID=) it assumes the short value.  Since it
is not clear to me the exact proprietary SPAM algorith,
the following suggestion should be taken with a grain of
salt:
 
1) Create or change List-ID= to the "old" / "short" name
2) Change the short name (requires list-maintainer involvement)
   to a non-lexigraphically first name
 
 
Your folks will continue to be able to post and alter subscription
info using both the old and new listnames.
 
I'm not sure what happens to searching archives though i.e.,
if both names work.
 
YMMY East and West of (the) Mississippi ;-)
 
/Pete Weiss in beautiful downtown University Park, PA