Question:

Is the Version-Specific Attachments feature irreversible in Vault? 

Answer:

Attachments are files related to Vault documents and do not take on the full features of a Vault document such as: document fields, workflows, etc.  These attachments can be associated with a specific document version. 

Once the user elects to configure the Attachments relationship as type source version specific, it cannot be reversed. Likewise, when choosing to make the Attachments relationship of type target version specific, this cannot be reversed.

Related Documentation:

Vault Documentation:  Vault Help