Comreg manage the spectrum but It is C na M who you would be dealing with to get a licence for broadcast.
Other radio services would be dealt with by Comreg directly.
You could approach Comreg about using 549 kHz and they might tell you it's cleared for use at 50 kW (or whatever), but they won't licence you for it.
Even if C na M awarded you a licence ( they might have to advertise it first), there's no guarantee you would be allowed the full 50 kW, (or whatever).