I'm looking for the rules regarding preparation and use of alternate versions of spells for D&D 5e.
If a spell caster prepares a spell that has alternate versions of the spell is the spell caster able to change the version of the spell to the differing version without needing to wait for the next day, or are they 'locked in' to casting the spell as the specific version they prepared?
We had a situation where the cleric of the group had prepared a 'Detect Evil' spell. But after encountering a specific NPC during game play the cleric announced that she would cast it as 'Detect Good' on the NPC. For sake of not stopping play to pour over the rules, and because I knew she wouldn't need to use any other spells during the course of that day I allowed her to use her spell as 'Detect Good'.
I do know the Sorcerer class does have flexible casting, so they don't have limitations on what versions they decide to use over the course of the day as long as they have the spell slots to cast it, but most other spell casting classes need to specifically prepare their spells for the day.