There is no way to run multiple MySQL installations using yum on a single instance. But, it's very easy to install and uninstall current and future versions via yum or rpm.
It seems you are going about this in a very wrong way. First do this on a staging machine. Document the steps and time taken in detail. Do this multiple times if you have to improving your steps each time.
 Backup your MySQL data using mysqldump
 Upgrade your MySQL to 5.6
 Restore the data
 Verify data integrity and ensure all your applications work
Then, do this on production server with the same steps as you did in your final staging trial.
Rollback is as simple as installing the current version of MySQL back and restoring your dump.
This way, you verified the upgrade works, you verified your applications work .. cPanel and what not.