Edit SIP Header and link to Avaya IP Office

[iainpg]

GoAutodial 2.1 from .iso
HP Ml360G7 Server on premise
No Digium/Sangoma Hardware
No Extra Software After Installation
Intel(R) Xeon(R) CPU E5649 @ 2.53GH

We have a really helpful Avaya engineer who kindly setup an IP extension "500" on his Avays system, we want to transfer agent calls to backoffice closers, we have been told to amend the sip header to display 500 and this will "work", we are only able to show the actuall 4 digit agent extension

Has anyone any experience in editing sip headers and can you shed some light, also any comments about tranferring to a IP office would also be greatfully recieved

Thanks

Iain