This is a tough decision. Frostbite seems like it would be much harder to apply than burn because of all the abilities and moves that can burn easily. And freeze, although it’s absolutely bonkers, is kind of balanced in the sense that you have no way to guarantee you are going to freeze your opponents and it’s more luck based, and the fact that very few moves can actually freeze.
If Frostbite is going to completely replace Freeze with no changes to anything else than I would probably say no, but if it does end up being added, I would add stuff like a Frostbite Will o Wisp or a Frostbite Flame body cause it’s more balanced that Freeze and is balanced enough to warrant it having easier ways to get it.
If nothing about anything else on what can apply Frostbite is being changed than no, but if there is going to be stuff like Frostbite Will’o Wisp and Frostbite Flame body than probably yes.
Edit: also, would this be coming in 13.5, or would it be coming whenever legends arceus stuff gets added?