If you want to transfer data between mendix apps, I would advise you to use appservices or webservices. You could create one module in Mendix with all your published and consumed webservices, including logic and pages for the configuration and import this one in every mendix app. After doing this, configure the target webservice url and credentials and start synchronizing data.
Of course I don't know what kind of data you want to transfer, but with webservices you could transfer small, large, complex or simple data. And in my opinion you don't have to create multiple target namespaces, because you're exchanging data between mendix apps regarding the same type of objects, so why would you maintain multiple wsdl's for every environment.
The mendix online platform offers a backup feature, you can actually use that to transfer data between environments. When restoring the platform asks you to specify a target environment; this no longer has to be the origin environment.
And you missed an app module that could be interesting: https://appstore.home.mendix.com/link/app/1624/Synobsys/Object-Backup-Restore