It is perfectly possible to point at several software repositories at the same time. To better deal with this situation, you need to use the yum repolist andyum-config-manager commands.

To get the list of all the available repositories (enabled and disabled), type:

# yum repolist all
...
repo id                       repo name                           status
base/7/x86_64                 n40l - Base                         enabled: 8,465
epel/x86_64                   Extra Packages for Enterprise Linux disabled
repolist: 8,465

Note: The -v option displays even more details.

To get the list of the enabled repositories, type:

# yum repolist
...
repo id                repo name                                          status
base/7/x86_64          n40l - Base                                        8,465
repolist: 8,465

To get the list of the disabled repositories, type:

# yum repolist disabled
...
repo id                       repo name
epel/x86_64                   Extra Packages for Enterprise Linux 7 - x86_64
repolist: 0

To permanently enable a repository (here epel), type:

# yum-config-manager --enable epel

To permanently disable a repository (here epel), type:

# yum-config-manager --disable epel

To temporary enable a repository (here epel) in order to install a specific package (here Pound), type:

# yum --enablerepo=epel install Pound

Note: Use the –disablerepo option to temporary disable a repository.

Source: Inspired from an ITSprite tutorial about the yum repolist command.