i really would suggest forgetting about the rheostat, i've had nothing but problems with them. they're wildly inaccurate and require too much tinkering. 104 is still much too hot for a ball python.
not sure if it will burn your snake, but it's not worth the risk.
invest in a thermostat. i think one of the cheapest ones is a Repti Temp 500R. i have a couple of them, they're much better than rheostats even if they're not as accurate as a more expensive proportional thermostat like a Herpstat or Helix.