PLAR would not be suitable for this. A translation pattern could match the dial pattern used on the fax machine which your users send fax from and add whatever digits you want and then pass the call along to a CSS that has visibility of the route pattern(s) you use for egress calls. That said you could do this with route pattern directly, so taking the route via TPs are not strictly required, although it would be recommended.
No I don’t know of a specific example of this, but it’s not really that complicated. You need to have a match that would catch what the user entered as the called number on the fax machine. For example a ! would work as the match. Then on the callled number transformation part on the route pattern you put 9 as the prefix. What is important to note here is that you would want to make sure that this is only visible to the endpoints that needs this, so you should put the RP into a partition that is only visible in the CSS that the fax machine FXS port uses.
Edit: Come to think of this one more time I recant my original comment about that it’s unnecessary complex to use a translation pattern. It would probably be easier and need less configuration if you were to pass the calls from the fax machines via a TP that matches !, ie everything, and then prefix 9 to the called number and send this to a CSS that sees your regular call routing where a 9 is needed. As before you’d want to keep this TP visible to only fax machines, so you’ll need to have the same PT and CSS construct as I previously outlined.
It depends on what type of setup you’re using in your VG. With SIP you could do it with voice translation rule(s) and profile that you deploy in the inbound direction on the specific voice-port. If you use SCCP or MGCP you can do it in CM on the individual port with the CSS having visibility of the partition that I outlined in my other reply.
