DD
You cannot participate unless you are registered and its too late to register. The event was open to 25 4x4s only and they actually received 30+ entries, so there are people on the stand by list already.
The only thing you can do is come and watch the event and get to know the organizers so that you are invited to participate next time they hold this rally.
By the way which 4x4 do you drive?
Regards
Sajidd