In my classic D&D campaigns, the question always comes up whether I will allow clerics (a.k.a. crusaders) to swap out memorized spells for “cure” spells as in the Spontaneous Casting rule from the d20 SRD. I have a hard time deciding.
Then, I came across this, which I find much more interesting. From AC 4: The Book of Marvelous Magic (1984) by Frank Mentzer and Gary Gygax, p. 16:
Prayer Bead: This valuable item allows a cleric to exchange one known spell (not yet cast) for another if both are of the same spell level. For example, if the cleric knows detect magic but needs cure light wounds, the cleric may use the bead to forget detect magic and gain knowledge of cure light wounds. The new spell may be cast as soon as desired. The cleric need not be fully rested to use the bead. After changing one spell, the bead disintegrates.
(For those not familiar with classic D&D jargon, “knows” means “prepared” and “forget” is equivalent to “lose” in the Spontaneous Casting rule.)
If these prayer beads were as available as holy water or—in some campaigns—healing potions, then it’s an interesting resource management mechanic. (Assuming you find resource management mechanics interesting. And classic D&D might be the wrong game if you don’t.) And it is more flexible too.
Trivia: In the original text, the name of the second spell was styled—both times—“cure light wounds”. I have assumed this was a mistake and put “cure” in italics as well.