How it is possible to copy a header (not embedded) from 300 into the following INVITE (recurse mode)

Hi,

This is my very first question here so hope I posted in the right place.

I came across this article, about the ability to have SBC parse an embedded header in the incoming 3xx response, and paste into the INVITE generated by the SBC post-redirection.

Ref: https://transnexus.com/docs/clearip-acme-shaken/

What puzzles me is the last paragraph, which reads…

You must use a separate approach to add a header manipulation rule (HMR) to copy the standard, non-embedded Identity header from the ClearIP SIP 302 response into the outbound SIP Invite to the called party. 
Using the HMR approach allows the Identity header to be passed in the 3xx response along with up to twelve routing destinations with UDP and TCP.