Yum can be surprisingly simple and frustrating at once. To add only one package from a repository you can do the following.
In the yum configuration file for the repository (normally this is /etc/yum.repos.d/$repository.repo).
You can also glob to include all packages of that type, such as:
Save the file, and search/install new packages. Yum will only see packages of “vlc” and nothing else.
If you are looking to do the opposite, the keyword is `exclude`. To exclude all rpms from a repository for instance:
Don’t add both exclude and includepkgs together without careful consideration.