I'm considering climbing everest without oxygen, and training by sleeping and running in an altitude tent which will lower my blood 02 sat. levels to ~70%. can i do both without brain damage?

No guarantees.: People have different susceptibilities to hypoxia depending on many factors including age, physical fitness, and health status. Also, the ability of the brain to withstand hypoxia is time dependent, so time at the summit will be critical.

Unwise: At prolonged levels of less than 90-92 percent there is a significant risk of brain injury from low oxygen levels. If you were to bring it down to the low 90's over months your body would compensate by increasing the number of red blood cells.

I agree and:: Part of the danger of everest is the traffic jam in the death zone. Waiting to access the fixed ropes on a good weather day hundreds of climbers line up, wait, ; are at risk of frostbite, low oxygen, ; hypothermia. There are many dead bodies up there who made poor choices or had rotten luck. Low oxygen has injured eyes, cost thought--resulting in the wrong life ; death decision when it matters.