Cold and Heat Resistance are registered as bad effects. This can cause unintended things, like Potion Core's cure, to interact with them.

Unless there's something I'm missing, there's no other kind of variable I can change for them, and AFAIK, cold/heat resistance appears on the same bar that other positive effects do.

Are you sure you're on the latest version of the mod?

This line, the true means isBadEffect.