You can do this but you’re probably better off doing it in the POM as others have said.
On the command line you can specify a property for the local repository, and another repository for the remote repositories. The remote repository will have all default settings though
The example below specifies two remote repositories and a custom local repository.
mvn package -Dmaven.repo.remote=http://www.ibiblio.org/maven/,http://myrepo
-Dmaven.repo.local="c:\test\repo"