By deploying this new package, will the DB modified correctly?
This is the entire purpose of the DDT. To deploy to a server (new or existing database) and have those structures updated without running scripts or having to deploy in a sequential order (in the event that there have been other releases between the current version and installing version).
Can I use this method of just importing the DB to the DDT with every new version of the DB I wish to deploy? Will it work?
Maybe....the reason is because this is not how the DDT was designed to work. The DDT was designed to import a database, but from that point forward the meta-data should be maintained within the DDT itself. There is a bit of logic that keeps up with the changes that occur so that an accurate depiction of what needs to be changed is logged. If you continue to make changes through SQL Management Studio and expect all of the meta-data logic to figure everything out, especially relating to data-type or field name changes, then you will have an issue.