Not practical.
The temps required to kill mold AND its spores would kill your precious plants much faster.
Trust me, just use serenade. Or whatever fungicide you find that is SAFE IN FLOWER. You have to get into the soil too to kill spores.
After this crop, empty out your grow room and bleach the fuck out of everyting, including your equipment.
Colder weather also slows plant growth.
The only time I would suggest using cold as a tool is to
-prevent mites from breeding while you are doing a treatment program to kill the little shits
-bring out the maximum purple in a purple strain, if purple is your primary goal.