I've been messing with retro/reentry with Mercury with failed gyros. In one occasion, I completely botched the reentry attitude; I was horizantal during reentry (saw it on external view) but I did not suffer any damage.
And in another occasion, I forgot to turn up the coolers in Mercury, and the cabin/suit/inverter temperature levels were off the chart. And again, I did not suffer any penalties.
So my question is: is it possible at this point in the development of Reentry to damage the spacecraft or injure the astronaut by mismanaging the ECS?