This appears to be the basis of the final fix soon to be released for the yum update vault EOL issue, ie to modify the original base and updates repositories
Refer bug 6873
db yum_repositories setprop base BaseURL '
http://vault.centos.org/4.9/os/$basearch'
db yum_repositories setprop updates BaseURL '
http://vault.centos.org/4.9/updates/$basearch'
db yum_repositories delprop base MirrorList
db yum_repositories delprop updates MirrorList
db yum_repositories setprop base status enabled
db yum_repositories setprop updates status enabled
signal-event yum-modify
yum clean all
yum update should then work correctly and normally
Edit: to be more exact, "will work correctly until a reconfiguration is done, at which time default values will return the repository settings back to original default values".
So the above solution is only a temporary workaround until an official update is released.
I did say it was the basis for the final fix soon to be released.
While suggested as being misinformation in bugzilla, I saw it as information that indicated to users what was being done to fix the yum update problem, so users could update older systems that were not "up to date" prior to an official fix being released.