Change the ID in the Saml response

[Klingenstein, Nate]

Stephen,

IdP v2.4.0 is quite unsupported at this point.  You're also dealing with
a special type of user information in SAML.

The question would need to be reformulated, though.  The SAML Response
ID should not be tampered with.  They want you to send email as a name
identifier with type persistent(which also shouldn't be done, but it
sounds like that ship's out to sea).

Depending on the SP's request, this is doable in 3.x with varying
degrees of difficulty and ugliness. 

It's doable in 2.4, but totally differently.  If I were you, I would
move to 3.x.  I know that isn't a small project, but neither is
supporting unmaintained software in production.

There will be many examples for this on the Internet with either
version.  Just search for ~ email address as persistent nameid shibboleth.

Hope this helps,
Nate.