"You know, according to this dumb sheet it says thirty four hundred to Round Hill --- is our minimum altitude..[but]..when he clears you, that means you can go to your initial approach altitude." Said the captain of TWA514 as he passed 3000' descending 1800', 30 miles out in the mountains of Virginia on 'approach' to Dulles.
Well as GF, aterpster and intruder have explained the FAA have nailed this one. You cannot leave assigend alt until established.
Despite suggestions it may be kosha in other countries, nobody has come up with a single reference to back that opinion. So the answer is still no.
On the other hand a 'cruise clearance' (USA again) clears the pilot for the approach
and descent to MEA at pilots discretion. But you don't get one of those whilst being vectored.