Can I make a local module with the Swift Package manager?

With the Swift 4 version tools, there's different means to do this-- where you don't have to provide a tagged version:

.package(url: "<path to repo>", .branch("master")),

See also: https://github.com/apple/swift-package-manager/blob/master/Documentation/PackageDescriptionV4.md

You can also use

.package(path: "path to folder")

if you don't want the overhead of an additional git repo. This can even be a relative path.