Like a electricity Wizard who casts lightningball instead.
They could just add rules that allow you to tweak the spells, just like how they allow for increasing damage with a higher spell slot. But also changing AoE size, changing damage type, range, changing needing to see the target, and other properties, ... All which you will have to chose when preparing the spell for the first time, not to overshadow metamagic and keep the game flowing.