A Problem with Red Hat's yum-rhn-plugin and a local repo mirror

Red Hat Bugzilla – Bug 746053: yum-rhn-plugin busted: Repository rhel-x86_64-server-5 is listed more than once in the configuration

Red Hat Enterprise 5.7 x86_64 kernel 2.6.18-274.3.1.el5

yum-rhn-plugin.noarch-0.5.4-22.el5_7.2

Running a cobbler-built local repository mirror for cobbler/PXE/Kickstarting
systems.  There are third party repos and a custom repo of locally required
packages.

After an update that changed me from yum-rhn-plugin-0.5.4-22.el5 to
yum-rhn-plugin-0.5.4-22.el5_7.2, I started getting failure on any yum command
with the message "Repository rhel-x86_64-server-5 is listed more than once in
the configuration".

I found the following workarounds: 

* disable yum-rhn-plugin by using "--disableplugin=rhnplugin" on the command
line

* downgrade to yum-rhn-plugin-0.5.4-22.el5 (yum-rhn-plugin-0.5.4-22.el5_7.1 has
the same issue) and put "exclude=yum-rhn-plugin" in /etc/yum.conf

It looks like an old bug crawled back into yum-rhn-plugin
Ref: <https://access.redhat.com/kb/docs/DOC-15495>

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Second question: Is there a way to do the equivalent of a yum-versionlock at the repository ?

I need to lock out yum-rhn-plugin at my local mirror rather than having to go to each client installed and downgrading the package.