You shouldn’t charge the battery when it is at freezing temp or below, this may damage it. It is best to charge any lithium battery above 40f. When the battery runs its cycle it is best to get it to a warm place. Storing a lipo battery is ok below freezing, however it is important to bring the battery up to 40-70f before balancing or discharge at load to warm it up before charging.

The only thing that comes to mind is setting the cutoff to stop sooner and discharge before charging. The only way to heat up the battery internally is discharging it.

Super light batteries are more susceptible to cold temps and slightly higher C rated and lower capacity to keep weights the same may help here. As temp goes down so does the C rating. However you still have to leave some capacity to discharge on the ground either by the plane or by a charger with a decent discharge rate.

The reason is as stated C rating drops with temps overall. You can discharge at lower temps so this is primarily where a higher C rated battery will help and if you are going to operate at sub freezing temps you may have to insulate the battery. If you are concerned about weight then a higher C rated battery at your current capacity will weigh more, if you are not then..,ok.
You ask how to charge in ambient low temps, and the only way is explained.. Either get a lipo bag with a heater of some sort, or operate your battery with a higher cutoff so you can discharge the battery further on a charger with a decent discharge rate. It is ideal to charge a lithium at room temp, and if you want to charge outside in freezing temps the battery of choice must have a high charge rate otherwise charging at 1c on a 2300mah battery may not keep it warm enough.
Lithium polymer and lithium ion batteries are extremely sensitive to low temps and some chemistries will get damaged if trying to charge a sub zero lithium