It does appear that the UW htcondor-stable repo does have 8.4.2 available:
condor1$ yum list condor-8.4.2
condor.i686 8.4.2-1.el6 htcondor-stable
condor.x86_64 8.4.2-1.el6 htcondor-stable
The baseurl is http://research.cs.wisc.edu/htcondor/yum/stable/rhel6
You should just be able to do a yum downgrade if you can reach that URL from your machine. Hopefully they’ll let you upgrade to 8.4.9 soon – I know how that goes.