No, it is not possible to specialize a node from a specialized node to the base type. Because in this way you are removing properties and the Alfresco model doesn't allow this type of operations using types. I suggest you to change your model adding some aspects that can be added and removed from a node. Each aspect will manage a group of properties and/or associations.
That's why for the content model you only follow an append approach: you can add definitions but you can't remove any definitions.
You can create a rule with an action (written in Javascript) that can be triggered to create a new node and moving the content from the old node to the new one.
But if you have a model based on aspects you can create your rule in a better way without creating new nodes.
Hope this helps.
