HGB, HCT, and RBC track each other. I don't know if there is a simple conversion between the three, but really any one of the numbers should tell you if you are in the danger zone or not. So if you are good on HGB, I wouldn't even worry about the HCT....
I remember BBB's self-phlebotomy thread here back in the day. He has more balls than I do lol
I try to go give blood every 3 months because TRT sends my HGB through the roof. Like I said, I have been too high to donate once and they sent me away. I drank a lot of water and went back the next day, and it was borderline still. No real good answer for guys that don't have it prescribed though.
I've heard doctors can prescribe phlebotomies, but I don't know how to go about convincing a doc to do that or where to even get it done.