The new domain model approach is basically based on the same core runtime but the upper mapping layers are completely new and rewritten. Also the enhancer previously was executed as a post-build step in Visual Studio and with the domain model approach it is executed as an msbuild task which works against the 'new' metadata. So the answer to your question is no, it is not possible for both approaches to work together.
Which part of the old model do you want to retain? If you can reverse map the database using the domain model approach and generate the classes you can still have your existing business logic, if any, in partial classes.The main work would be in tweaking the mapping between the object model and the relational model, in the designer.
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