How do I filter an entityreference field based on other fields?
Your question reminds me of this similar question you may or may not find it relevant.

Alternatively, you could use Masquarde


  The Masquerade module allows site administrators (or anyone with
  enough permissions) to switch users and surf the site as that user (no
  password required). That person can switch back to their own user
  account at any time.


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