Is it possible to have this backpack keep items cold when in the cold biomes but not in the warmer ones? I know there's the permission for all the time.

I'll look into it to see how feasible this is.

Sorry for the delay. I implemented changes to address this. You can beta test it now by downloading the plugin from the GitHub repository.
https://github.com/WheteThunger/Backpacks

I apologize I saw this when at work and then promptly forgot until now to test it. It works as stated. It updates after a couple seconds while in noclip.