Now they can "officially" do it.
This test reached 10 times the altitude of the international space station. They could hit the majority of countries on the planet with nuclear weapons.
This is meant somehow to magically be a deterrent?
Not quite yet.
They first need to reliably be able to target population centers with nukes sufficiently miniaturized to be carried on one of their ICBMs. The deterrent is not credible until it is publicly confirmed -that's the whole point. NK would have to launch an actual nuke to a publicly pre-announced test site. An uncertain deterrrent is actually inferior to no deterrent at all; it incentivizes a possible preemptive first strike.
The entire NK program should have been carried out in secret, like that of Israel. Israel's nukes are not a deterrent per se, just a doomsday response to potential adversaries. But NK has made the mistake of putting itself into the spotlight before all its ducks are in a row.
(Note: a truly credible nuclear deterrent requires the ability to launch from subs that are invulnerable to a pre-emptive first strike. A second [poor] choice would be a fleet of bombers, some of which are always airborne.)
The US won't launch a preemptive first strike nuclear attack against NK. It would destroy all the existing alliances in the region, and turn SK against the US. Even a conventional attack would end up killing thousands of South Koreans and US troops. Bannon has shot this done as stupid. The only leverage Trump has is convincing Kim he is actually stupid enough to launch a military strike - the madman theory is acutally the stupidman theory.