Sorry for the premature post, everyone.
I just found this on Microsoft's site.
"If you use the MDSModelDeploy tool to update an existing model and its data, and the package does not contain an entity, attribute, or member that exists in the destination model, MDSModelDeploy will not delete that entity, attribute, or member from the model."
https://msdn.microsoft.com/en-us/library/Hh479646.aspx