Does a spell made permanent by Permanency stack with another permanent version of itself?

Question

This question was brought up recently by a player in our Pathfinder group who was planning to use the Permanency spell on the Resistance spell at later levels (applying the price for permanency and all of that) to simply upgrade the party's Fortitude, Will, and Reflex saves over and over again, effectively raising them all by an additional +1 each time. And, more to the point, that player wondered if you could continuously and repeatedly make this spell permanent on a single character or creature. Our group couldn't find anything in the spell rules for Permanency and Resistance.

We considered which spells might be stackable that we know are affected by Permanency, like Reduce Person or Enlarge Person spells; ultimately, we found that for those spells in particular say in their spell descriptions that they cannot be stacked, while the description(s) for Resistance (and of course, the Permanency spell itself) do not.

TL;DR, the question I have is as follows: Can a spell be made permanent on a character or creature more than once to stack the effects of that spell, provided the spell's description does not disallow stacking?

I'd prefer RAW answers, but any answer regarding rulings will do.

Answer 1

"Can a creature employ the spell permanency to make permanent the same spell more than once to increase that spell's benefit?"

Usually no. Most spells with ongoing effects don't combine with themselves for greater efficacy. Instead, a spell does what it says it does, and only does what it says it does. This idea is covered in greater detail on Combining Magical Effects.

For example, the resistance spell grants a creature +1 resistance bonus to its saving throws. A creature affected by a second resistance spell gains the same +1 resistance bonus to saving throws that the creature had already received from the first resistance spell. (However, the creature would use the longest duration among the resistance spells cast upon it.)

"What if the the spell's description does not disallow casting it on a creature multiple times to increase the benefit the spell provides?"

In a game that relies on exception-based design, things work according to the rules except when the rules say they don't. This means a spell needn't specifically disallow multiple castings providing an increased benefit. Instead, a spell must specifically allow it to be cast multiple times for increased effect! This, too, is covered by Combining Magical Effects.

There's some debate whether the same spell can affect the same subject multiple times if each spell has an entirely different effect each time (e.g. resist energy).

On the resistance spell

The resistance spell specifically won't stack with itself because it grants the subject a named bonus. For more information search the Glossary for the entries stacking and bonus.