P-Asserted ID with Nextiva, use with different CIDs

I am using this code

exten => s,1,SipAddHeader(P-Asserted-Identity:<sip:${CALLERID(num)}@bt.voipdnsservers.com>) exten => s,n,MacroExit()

to add the caller id to the SIP header, but I need an extension this one being ext 4012, to dial out of a different CID, but with this code I am assigning this PID to all the extensions. How can I add a specific PID to an extension?