quick Google search for Cuir Boile brings this simple description on Wiki:
"Boiled leather, sometimes called cuir bouilli, was a historical construction material for armour. It consists of thick leather, boiled in water (some sources hold that oil and wax were used as well, others posit the use of ammonia from fermented animal urine[citation needed]). The boiling causes the leather to be harder and more brittle. The boiled leather can be fashioned into lames/scales to make lamellar or scale armor. Or, because the leather remains flexible for a short time after boiling, it can be molded into larger 'plates'."
The leather gets hard, it can be brittle.
If you get it too hot, it scorches and curls.
If it was originally chrome tanned, ir turns into a shrinky dink.
OTOH, this works great for making a leather bottle - so long as you never fill it with hot drinks or high test booze. (alcohol can break down the wax)
As you the other question - yes, I've heated knife sheaths with a hair dryer - or over a floor vent, smeared then with a thick coat of sno-seal, then used the har dryer to melt in the wax. After it cools, buff it with a soft cloth and you get a nice satin finish.