We can upgrade or downgrade the packages using yum or rpm command in Linux and unix system. There are two way roll back an rpm,

RPM
YUM (If the yum command support)

Downgrade use rpm:

If you want to downgrade the rpm package can do without uninstall the packages. The following command can help you,

$  rpm -U --force rpm-4.9.1.3-6.fc17.x86_64.rpm

or
 
$  rpm -ivh --force rpm-4.9.1.3-6.fc17.x86_64.rpm

    Same as using --replacepkgs, --replacefiles, and --oldpackage. 
 
$  rpm -Uvh --oldpackage package1.rpm  package2.rpm

--oldpackage, option is allows to install older versions.

 -U means "upgrade" this option also will replace the other version. If you will use -i instead of -U  both versions installed.


Downgrade use yum:

Also downgrade the packages using yum command, This command will  remove the packages that depends on the current version of the package.

yum dowgrade package-name

For example will remove a vsftpd package from the system,
 
$  yum downgrade vsftpd-2.2.2-14.el6

or
$  yum --allow-downgrade install package-1.1.2


Finally, If you dont want to downgrade a specific package, yum will need to know not to upgrade this package

open the yum configuration file and add the package name with "exclude"
 
$  sudo vim /etc/yum.conf


# exclude packages from updated

exclude=mysql