Is there a word for when a mechanically identical card gets new creative in a new world? Like Searing Spear>>>Lightning Strike, or Glory Seeker>>>Traveling Philosopher. I've seen it happen more often the past few years. It's not like color-shifting (prodigal sorcerer>prodigal pyromancer).
We usually call those “functional reprints,” as the function (mechanics) of the card remains the same but the flavor treatment is different. We do it when design or development likes what the card is doing for the set mechanically, but Creative has some reason to change the flavor (to express some aspect of the setting, for example, or to create a more fantasy-resonant card).
Some cards (such as both of the cards you mention) had other rules text at an earlier stage of development, got their art commissioned based on that text, and then had their mechanics change to become functional reprints of some other card. The card that you know as Lightning Strike was something else for a while, then was changed to become functionally identical to Searing Spear. But by that time it already had art of a bolt of lightning (rather than, like, art of a fiery spear or spear-shaped blast of flame), so couldn’t be called Searing Spear. That’s another way a card can become a functional reprint.