This would be a great addition to the Swift Package Manager.
Personally I would slightly favour add as command. Though perhaps install is more common amongst package managers.
Being able to use something like ...
$ swift package add github.com/foo/bar@1.0.0 -t TargetName
... would be a real time saver. This would add the Bar dependency (version 1.0.0 specifically) only to the target named TargetName.