iax_general_additional.conf

iax_general_additional.conf says the following

; do not edit this file, this is an auto-generated file by freepbx
; all modifications must be done from the web gui

disallow=all
allow=ulaw
allow=alaw
allow=gsm
mailboxdetail=yes
tos=ef

my question is where does it get the allowable codecs. i would like to try some different codes out but is says not to edit this file and when you change it and rework a trunk it erases your changes. Where in freepbx can you add a different codec.

thanks
rusty