Re-skinning Spells

As with Re-skinning Monster you can do the same with spells.

What that means is take the classic fireball spell and make it an acid ball.  What changes? the damage type mainly. You can increase the detail and go will splash damage the round after, but that changes the spell by increasing it's damage. A simple way is to decrease the damage by the fireball by two dice and then adding an effect of two dice damage the round after (one dice if you made the save)
Pretty simple.

Examples are,

Burning hands to Lightning damage (if you want to add extra damage to armoured targets lower the DC for it and add a dice damage, or you can give disadvantage to the save for armoured targets.

Ice Knife to Poison Knife same spell but explodes in poisonous damage.

Thunder wave to Necrotic wave, same spell but is Necrotic damage.

you get the picture.

Enjoy!