If you need to, as a once-off, disable specific repos (e.g. if the version of a packages you need are in a lower-priority repo), or if you need to enable a specific repo (which is disabled by default), you cna use the below.
yum install --disablerepo="base,epel,oem,puppetlabs-7,puppetlabs-7-dependencies" --enablerepo="base7.2" --installroot=/mnt/rootfs pciutils