At the moment it is not possible to export/import the sources from the Developer Portal CMS.
There is a need for a CMS API which would allow to:
• Download single files (incl. by name)
• Upload single files (incl. by name)
• Publish the current state
• Revert the current state to a previous version

This would be useful for the following use cases:
• move the complete CMS from one 3scale account (instance in on-premises) to another one
• manage the assets (templates, CSS, images etc.) externally (under version control) and upload them automatically to 3scale

Additional requested features:
• Download all CMS sources as zip file
• Upload all CMS sources as zip file
These should be available in the UI.

Additional Notes:

Some customers have used the undocumented API and unsupported tools to use the API to do exactly what they want. They have a DevPortal template which they use to automatically create new dev portals for new APIs on-demand, and then they link them into their overall (hand built elsewhere) API Catalog.