Lighting a fire at Tara would almost certainly be a prosecutable offence as it's a National Monument and protected by law (even if the valley below isn't protected as it should be!) I hope nobody's thinking of lighting a big fire on a protected monument to highlight how poorly other monuments are being treated.

The use of the beacons died out a long time before the use of Lugnassa sites and so they aren't that well documented. I can't remember where I read it, but I did read a theory that most of the Lugnassa sites were previously beacon sites, which makes sense as most of them are high up.