From 72 to 32 is 40 degrees, from 72 to 372 is 300 degrees also the expansion of aluminum is much greater than the contraction of steel. Freezing the bearing will do almost nothing except create condensation, not recommended.
First thing is to clean the recessed area so the bearing can come out and remove the wheel studs. When you heat the hub, heat it quickly before the bearings absorb too much heat and expand. Pre heat the oven to 400 then put it in for 15 minutes, if it doesn’t go, put it back in for 10 min. It will get smokey from the bearing grease.
If it’s still difficult, move the spacer to one side then knock the bearing out by hitting the inner race with a drift punch or steel rod. Don’t let the bearing tilt too much. Once the first one is out the spacer will fall out to give you access to the other bearing. Work quickly as heat will be transferring to the bearings.
Pressing in the new bearings can be done cold. Press the bearing that sits flush first until it seats. Drop in and center the spacer. The second bearing is where the magic happens. The inner and outer races of both bearings have to be held in alignment. The proper pressing tool will center the spacer while pressing the inner and outer races evenly until it seats on the spacer. Now when you tighten your axle nut there is no pre-load on the bearings.
You can drop them in by heating the hub and maybe get lucky but if you tighten the axle nut and the hub binds up you’ll have to try again and heating the assembly to get the bearings out hurts the grease.
Hope that helps,
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience