[Zeke]

Glazing putty works fine in cold weather as long as it's 70* itself. Just put the can of putty in a warm spot a couple of hours before use. Warm, not hot.

You can locally heat the old hard putty with a BBQ starter, the kind made out of an oven rod. If you don't have one of those, maybe you have an old style soldering iron. Open flame is too hot and spoils all the nearby paint.

Also, if you are using an open flame and get it too hot, the glass can crack and you will have glass splinters do deal with. So be prepared and wear gloves and glasses.