Cold is just to stop losing the pressure. Once the cap is on, the cap will hold the pressure (if you haven't overfilled it) and the bottle can be slowly warmed safely.
FWIW, we seal apple juice in champagne bottles, then boil them in a rocket stove to pasteurise. They don't break during this treatment, I think you'll be fine.
FWIW, we seal apple juice in champagne bottles, then boil them in a rocket stove to pasteurise. They don't break during this treatment, I think you'll be fine.