When using ldapadd there frequently is an additional line of information following the "unwilling to perform" message that contains more specific information about the problem. If you have not tried using ldapadd that would be a place to start.
Doh! Don't laugh too hard.
I was trying to update my "test" server, which was set up as a syncrepl client, and therefore was in read-only mode.
Once I copied the schema updates to the main server and then attempted to update there, it worked correctly.
Tim Gustafson Baskin School of Engineering UC Santa Cruz tjg@soe.ucsc.edu 831-459-5354