Flame Weapon and Darkfire have been adjusted to use reagents. This means casters can adjust the damage type affixed to the affected weapon. Fire, cold, electrical, positive, negative, and acid energy are currently available.
Flame Weapon and Darkfire both work like this; both can also now be Empowered and Maximized. There are in-game ways to discover the appropriate reagents, so it isn't entirely trial by error. As with any custom content, please report anything unusual with the spell that may result in exploitable or over-powered behaviors.