Adding an account code when dialing our gateway

Our Asterisk system supports more than one companies. Our Gateway Provider can bill each company based on an Account Code sent out with the Dial. I used the CDR Account Code and did a little patch to the [macro-dialout-trunk] to send the gateway AcccodeDialednumber. This has been working great until I decided to use a newer version. I patched [macro-dialout-trunk] to do this.
[macro-dialout-trunk] is no longer in extensions.conf and has moved to extensions_additional.conf where one cannot edit it.
Any ideas or suggestions on where else to do this?

Here is the code in the older version I added to /etc/asterisk/extensions.conf under [macro-dialout-trunk] as follows:

; Special mod for custom account code
exten => s,n,Set(CODE=${CDR(accountcode)})

exten => s,n,GotoIf($["${custom}" = “AMP”]?customtrunk)
; Modifyed next line
;exten => s,n,Dial(${OUT_${DIAL_TRUNK}}/${OUTNUM},300,${DIAL_TRUNK_OPTIONS}) ; Regular Trunk Dial
exten => s,n,Dial(${OUT_${DIAL_TRUNK}}/${CODE}${OUTNUM},300,${DIAL_TRUNK_OPTIONS}) ; Regular Trunk Dial w/ Account Code
exten => s,n,Goto(s-${DIALSTATUS},1)

Thanks in advance for the help…

New version added [macro-dialout-trunk-predial-hook], it is just before the dial happens.

So I added the following in extensions in the [macro-dialout-trunk-predial-hook]

; Special mod for custom account code
exten => s,1,Set(OUTNUM=${CDR(accountcode)}${OUTNUM})

Works great.

Left it here just in case someone else finds a similar situation and need help.