You have to be on a Heavy (HR) or Medium (MR) licence for at least 1 years before you can get an articulated licence HC or MC, so no, you can't decide tomorrow you want to drive road trains. You have to do a course that provides a certificate of competency and then pass an on/off road driving test for the HC/MC licence. The hardest part in the reversing into bay tests I found, nailed it first time, but its not simple. And yeah, turn up without experience for a job where you are driving half a mil to a mils worth of rig let alone cargo value, you know the answer to that. Getting good drivers is the issue, not just getting anyone.
That being said you don't have to do anything with your licence for that 1 year before attempting the HC/MC course.
Correct me if I'm wrong, but aren't the VA pilots on about 17% less than pre administration?
Some mates I've spoken to say they're on 25% less since admin, due to work practice changes, hence why comparing base salaries is irrelevant in airline work.