In current version of Umbraco, if I dump all my document types to a package then install on an existing instance, will it tell me if I'm overwriting anything?

What I'm looking for is a way of applying a package of document types from a test site to a live site, but only applying changes; so adding new types, adding properties to existing ones.

Unless I'm mistaken, applying a package will just overwrite everything, thus unlinking existing content from any document types, is that correct?