Well, this should tell you what's installed for yum:
rpm -qa|grep -i yum
Theoretically you could make a note of all those, try
rpm -e yum*
-e = erase
and make notes if it says its going to remove dependencies as well. You'll need to re-install every rpm mentioned in one cmd.
You could also look at
rpm -V yum
first, to see what it says. See man rpm.