Is a diploma updated in new request?
Will the university reprint the diploma with its original signatures or generate a new diploma with signatures of current university officials?


The policy depends on the university.  For example, replacement diplomas from Harvard include the names of the officials who were in office at the time the original diploma was issued, but without signatures, while those from Stanford include the names and signatures of the current officials.  Some casual web searching suggests that Stanford's policy is more common, but it's certainly not universal.


  However, a diploma does not have issuance date (only the date awarded). 


Reissued diplomas are typically marked as such.  For example, this is part of both Harvard and Stanford's policies, and web searching suggests it's very widespread.