changing email addresses of subscribers

The majority of the users on my list will be changing their
email 
addresses this summer.  Is their a way I can do a bulk
process change of 
the email addresses since the beginning part of the email
addresses will 
remain the same and only the part after the ""
will be different.

Also, how do I search and eliminate the addresses of users
with out-dated 
email addresses? 

Thanks!

Melissa Jacobs Israel
mjacobs7nycboe.net 
NYC School Library System

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