The train that you have got there csyjunior is VN12 minus a car running tests. N class locos are unable to run push/pull configurations, I am assuming that because VN12 is minus a car they have attached an N class loco to replace it for the test.
Here we go with infactual information and outlandish assumptions again!
N Classes ARE
able to run in push/pull configurations, having done so for the Avalon Airshow specials since at least 2001. Their dynamic brakes can't be used when in this mode though.
The train csyjunior
saw was VN12's test run out to Geelong ex Newport Workshops, which provided all went well, should have proceeded onto Southern Cross; the set to enter service at a later date.
Only four of the five cars (ACN36-BRN35-BN23-BZN273) have been completed so far, the fifth, BTN268, is not due out at this stage for another month.
N458 lead the train as a test; making its first appearance out of Newport Workshops since the 23rd of October, after having an Intermediate Component Change out and some other works completed on it.
N451 came along for the ride, and presumably, as a backup in case N458 had problems. Getting out of Newport Workshops and onto the mainline would have been easier with locos at both ends of the train.
I believe wongm
saw it too; I messaged him regarding it and he replied saying he was trackside.