Not sure about the specific health risks one could get if they snorted a dead person's cremated ashes ^{[that's a comment I never would've thought I'd make on reddit]} I mean it would obviously affect them in some way but I'm no doctor, perhaps it would cause a blockage in the person's upper nose or cause a headache or some sort of swelling, idk.

In regards to injecting/eating cremated ashes. I watched a documentary years ago about this person who had OCD and had a thing for eating the cremated ashes of their pet/partner and IIRC the documentary basically said that the primary health issue that could arise from consuming cremated ashes was blockages in the organs because when ash is wet it will turn into a thicker substance and can turn into a concrete-like substance when dried, but idk if that last part is true or not. I suppose it would largely depend on how much cremated ash the person would consume, if they were to eat a handful of cremated ash or something like that then yeah it probably would cause some sort of blockage or build-up to one atleast in the person's organ(s) eventually.

Snorting ash though, no idea what may happen, injecting it? would probably depend where and how much cremated ash is injected, if you injected too much ash into a vein then I'd assume you could end up giving yourself a clot or something if the ash creates a blockage and that would most certainly fuck you up if it didn't get fixed in time or didn't break off by itself.