slapdmodify(8) is the (nearly untested) result of non negligible cut'n'paste.
In any case, there seems to be significant side code commonality between slapadd and slapmodify, basically everything related to syncing the context entry. Maybe we should move that code in helpers in slapcommon.c.
See ftp://ftp.openldap.org/incoming/pierangelo.masarati-2010-12-06-update_ctxcsn.1.patch.
p.