1. Instead of getting sick from radiation, ghouls get buffs related to their radiation level. Damage resistance, damage output, speed, and stats could be improved. Ghoul players have the greatest buff at "Critical" radiation. The benefits are less at "Deadly" radiation, and they die at 1000 rads as usual.
2. Ghoul players automatically eliminate radiation at a rate of 1 rad per 5 realtime seconds. Meaning that if you have 300 rads, it will take 1500 seconds (25 realtime minutes) to get to zero.
3. If a ghoul player reaches zero rads, their hitpoints are metabolized instead at the same rate. Without the life-sustaining radiation that their bodies depend on, they begin to weaken and die.
4. If a ghoul is injured, radiation is converted to health at a rate of 1/20th of missing hitpoints every 5 seconds, plus a bonus of +1 per radiation level. While healing, radiation is metabolized at a 1:1 ratio according to health granted. In other words: If the player has 200 maximum hitpoints with 50 current hitpoints, on the next script run they will regenerate 200-50 = 150 / 20 = 7.5 hitpoints, then plus 1 per radiation level. If they at Moderate radiation, their bonus is 2, for a total 9.5 HP regenerated in exchange for 9.5 rads lost.
5. Ghoul players suffer a 50% reduction in healing effects from stimpacks. Their odd physiology does not respond as strongly to baseline human to the healing chems.
Numbers open to adjustment of course to strike a balance for playability. The practical upshot to all of this is that ghoul characters should be more durable than other characters provided they are strongly irradiated, but a ghoul will always be looking for places to "charge up" lest they wither away.