Technically it is possible, by some custom listeners/code which will run when a pirep gets filed.
But it is very tricky, because aircraft developers and livery painters mostly not paying attention to aircraft icao codes or aircraft.cfg entries, most of them are even not able to spell airline names/codes properly in the liveries they ship. As an example to false icao codes being used by developers is PMDG 737 series, even though they ship A B738 (B737-800) to people, their aircraft config says it is a B737 (B737-700), same applies to B736 and B739 too. Also MSFS has other problems converting/using the livery aircraft.cfg entries to plain text and reports back strange codes (their variable names) back to 3rd party addons like vmsAcars.
In theory, vmsAcars returns back the aircraft title to your phpVMS/server as a pirep field value, with a custom listener/code you can check the livery name and do whatever you wish (like penalizing the pilot, rejecting the pirep, commenting on their pirep etc.) even though you will have lots of false positives it is possible.
However to reduce those false positives, after you have your custom listener up and running, you can ship your liveries to your pilots, which will have correct aircraft.cfg entries and kindly force them to use your officially approved liveries for flights. Rest will continue creating problems, but will be rejected automatically, which is another nice way to teach people to follow VA SOP and rules
One of my addons (Disposable Basic) offers an auto rejection feature, if you need something to begin with, you can check its code as an example to build your own.
Hope this helps