Another way is to assign to a substr() that's off the end of the string.
-=item Modification of noncreatable array value attempted, subscript %d
+=item Modification of non-creatable array value attempted, subscript %d
(F) You tried to make an array value spring into existence, and the
subscript was probably negative, even counting from end of the array
backwards.
-=item Modification of noncreatable hash value attempted, subscript "%s"
+=item Modification of non-creatable hash value attempted, subscript "%s"
(F) You tried to make a hash value spring into existence, and it couldn't
be created for some peculiar reason.