So, let's say we want a mage character based on ice, sure, there are quite a few spells with Cold damage/thematic, but they're not quite what you want… You want him to have a Fireball that deals Cold damage, you want a Frostball, Iceblast, Frost Explosion, call it whatever you want!
So, if I took spells like Fireball, and changed the damage type to ice and the saving throw to CON, would that affect the game balance?
Another example, let's take Sunbeam and turn it into… Darkbeam? It now deals necrotic damage instead of radiant.
I'm aware of this question: What are the most and least-resisted damage types?, I know that a Fireball that deals Psychic Damage and requires an Int save is stronger.
So let's classify saves in two categories: The "common", Dex, Con and Wis, and the "exotic", STR, INT, CHA.
So, if I swap "similar" damage types (fire/cold, necrotic/radiant, etc) and also swap saving throws of the same "category" (Dex => Con/Con => Wis, etc) would that mess up game balance?
Best Answer
WoTC have released an Unearthed Arcana Wizard subclass called Lore Master. One of the features this subclass gives is:
This seems to cover both effects that you wish your Mage type character to have.
So WoTC appear to be looking at the same sort of concept that you want for your homebrew campaign.
Looking at this trait however it is evident that WoTC, at least, consider the changing of damage type to be not that big of a deal to game balance, but the changing of the type of saving throw to have a potentially greater effect (and thus needed to be restricted).
Taking your fireball example, changing the saving throw from DEX to anything else would eliminate the rogue’s evasion class feature.
In general the saving throws have been sculpted to the type of effect the spell is imposing.
Some salient examples are:
Important Caveat
It obviously comes with the caveat that this subclass hasn’t been playtested as extensively as the subclasses published in the books, and as a result is not necessarily balanced within the game.