There are benefits to acquiring Azure Services through CSP – your Azure resources (virtual machines etc) can all be managed by a partner and you can pay monthly for what you’ve actually consumed. So, can you migrate an existing Azure Subscription (and all your resources) in an EA or Open agreement, for example, to CSP? The short answer? No. You need to move resources from the old Subscription to the new one manually.
For more information – and instructions – this Microsoft blog post is well worth a look: http://bit.ly/2lvwn9l.