Kobold Avenger
Legend
While they've hinted at Planetouched Tieflings being different from the PHB Tieflings, and a couple of books such as Sword Coast Adventurer's Guide and Mordenkainen's Tome of Foes did try to introduce some variants and subraces. The Planetouched Tieflings in the Planewalkers Handbook are a varied subrace with many variations on appearances and abilities, as they could not only come from Devils, but also Demons, Yugoloths, Gehreleths, Hordelings, Night Hags, and other fiends or just plain mutations from Lower Planar influences.
Going by some of the guidelines from Tasha's Cauldron and expanding it a bit more, I'd allow not only exchanging ability scores and skill bonuses, but also spells for other spells of the same level and fire resistance for another type of resistance, for a quick and easy version of how to handle Planetouched Tieflings.
Though for further things like flight (if allowed) it's exchange that for all spell-like abilities, or allow it to be learned later as a feat. While some things like Light Natural Armor (AC 13) or Natural Attacks such as Claws might be exchangeable with Fire Resistance.
Going by some of the guidelines from Tasha's Cauldron and expanding it a bit more, I'd allow not only exchanging ability scores and skill bonuses, but also spells for other spells of the same level and fire resistance for another type of resistance, for a quick and easy version of how to handle Planetouched Tieflings.
Though for further things like flight (if allowed) it's exchange that for all spell-like abilities, or allow it to be learned later as a feat. While some things like Light Natural Armor (AC 13) or Natural Attacks such as Claws might be exchangeable with Fire Resistance.