Let's say an evil creature has learned Protection from Evil (or has it available to cast via a wand). Given that it has the [good] descriptor,
- Can they cast it on themselves? (I believe so, unless they have a class that prevents it, or some other rule specific to that creature)
- Are there any side effects? (e.g. they gradually find themselves gaining more "good intentions?")
I know that casting spells with the [evil] descriptor (e.g. Animate Dead) can corrupt a good or neutral being…but it seems odder to think of [good] spells redeeming an otherwise evil being.
(I was just searching the pfsrd and couldn't find the rules describing the effects of [aligned] spells. I'd love a link to that as well, assuming one exists. Thanks!)
Best Answer
Yes, evil creatures can cast Protection from Evil. You can cast spells with whatever alignment subtype you want, it's just that there may be consequences. Unless the caster is a member of a class whose description says explicitly they can't do that... Like the cleric for instance. Since casting an alignment typed spell directly taps into that raw goodness/evilness/etc of the universe they just plain can't do it.
The Alignment section of the PFSRD states that casting [evil] spells is the equivalent of committing minor evil acts (third sentence).
I would say that casting [good] spells, like casting [evil] spells, has the main primary effect of pissing off your deity if you're on close terms with them. So if a good divine-type is casting [evil] spells (or otherwise committing evil acts) they may get punished, same deal with an evil divine-type casting [good] spells or committing good acts. "Hey, I thought you were on board with the program, maybe some spell failure will wise you up."
But for longer term alignment change, you're right that it's not just "cast a bunch of good spells and you're good." Even though the alignments are depicted on a symmetrical axis, they aren't. Evil is a corruption of good, good is not a corruption of evil. Some people like treating them just like they're different football teams, but that's obviously not the case in the source material of real world religions this is all being drawn from.
There's a new section on Changing Alignments that is directly relevant to this interpretation. An evil creature has a specific path they would need to follow to become good and a set of penances they would perform to get there. Conversely, there's a lot of paths to becoming evil. "Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. But small is the gate and narrow the road that leads to life, and only a few find it." Or, for those fans of the second most popular holy book (TVTropes), Evil is Easy.
See Is casting the spell Blood Transcription an evil act? for related discussion.