In 10.4 you cannot modify the objectclass of existing users. This is a change in the underlying OpenLDAP 2.2 code.
To make changes, you will need to pull out the account and re-add it with the appropriate objectclass info.
You could feasibly add the radiusprofile schema to an existing schema file, but in this case you are supposed to drop your LDAP database and re-add it.
-Matt