I don't know anything about stone tablets or anti-existence, but I tried to go beyond existence myself by more traditional means. It's obviously very hard, I find it is something like becoming undead all over again but on a different level. Unfortunately I mostly get stuck at the top of existence or I start to drift off into the hell of no-self and non-existence which is of course a grave mistake.
When you became undead, you had to enlighten to something. You had to go beyond the duality of life and death. You went beyond life and by default also beyond death, becoming "immortal" in the process. But it was not too hard because you could see that beyond was still existence, so you went beyond the duality of life and death and you still exist. You realized that duality was bullshit. Now I think it's the same with the duality with existence and non-existence. But this is more like a plunge into the unknown, into the ultimate darkness since we usually cannot see what lies beyond to catch us safely. At least I find it hard to see beyond. The fear that you stop existing is imo bullshit because non-existence is a part of the existence duality which you will go beyond completely. Lust like the fear of death was bullshit when you went beyond life to become "undead". But then again what is there, and what will we be? I still struggle with how to actually go beyond existence and/or be beyond existence. I only feel like once you make the leap you will be truely eternal, and not even existence will be able to lord over you. You will be able to freely drop in and out of existence as you please. Who knows?