If the grid-mapfile is being maintained by a separate mechanism, it's
likely that the grid-mapfile-add-entry and grid-mapfile-delete-entry
commands could either interfere with that mechanism, or that any
changes made could be ignored or clobbered.  

In the case of gx-map, the grid-mapfile is normally
maintained with its permissions set to 444, so attempts to run
grid-mapfile-{add,delete}-entry will normally fail anyway.  However,
gx-map can be configured to use different permissions, and it would
be nice to have a more meaningful error message (so someone doesn't
"fix" the problem by doing a chmod).

Note that I've never actually run into this problem, or heard of anyone
else doing so.  Some people have attempted to update a grid-mapfile
by other means and had their changes clobbered by gx-map, but that's
not a grid-mapfile-{add,delete}-entry problem.

A grid-mapfile generated by gx-map will always start with a comment 
block like this:

#
# Automatically generated by gx-gen-mapfile (gx-map 0.4.1)
# at Thu 2005-03-24 05:49:19 UTC on lutefisk.sdsc.edu.
# Do not edit this file.
#

I suggest that if the string "Automatically generated" appears 
in a comment in the first few lines of the grid-mapfile, the
grid-mapfile-{add,delete}-entry commands should refuse to attempt to
modify the file, and should print an error message indicating that
the grid-mapfile should not be modified.  Tools other than gx-map
could then adopt the same convention.