YUM is a nice (and useful, when used correctly) tool to manage packages, using RPM as its engine. APT, the Debian alternative, has this ability, and so does YUM.
YUM does not pin a specific version of a package, but rather avoids upgrading it as soon as it was marked. It remains installed, but never will it be upgraded, even if other packages require a specific, newer, version of this package.
This “upgrade prevention” can be done using the directive “exclude=” inside /etc/yum.conf, where the values are the names of the packages (wildcards can be used!), space limited.
And a big “thank you” to Omer, who have pointed out my mistake. Too much NIS lately…