The title seems unclear, so I will try to explain it. (Also, feel free to change where this thread goes; not entirely sure where it falls under.)
Paladins and Anti-Paladins have some similar abilities and spells, some not really. However, some of these differences are key factors. For example, Paladin spells usually provide a Sacred Bonus, whereas Anti-Paladin spells have a Profane Bonus.
Again, some spells remain similar, others not so. Those others have primary restrictions due to type bonus differences. A proposition I come up with is to provide minor differences between these spells/abilities that aren't in common with the opposing class, and ultimately add what is the same spell to the other list.
The real question boils to this: Is a spell that has no opposition comparison being transferred to the other class a game breaking factor?
I'm sorry, I have no idea what you're asking.
I can't imagine it being a big difference in the long run of things. I'd recommend allowing it with the condition that if unexpected conflicts appear down the road you reserve the right to reverse the ruling... easy enough since we are talking divine spells after all.
I'm sorry, I have no idea what you're asking.
Let's say a Paladin-only spell provides a +X Sacred Bonus to Y.
Is it unreasonable to have it function as an Anti-Paladin spell to provide a +X Profane Bonus to Y (and when the opposite occurs, the same role applies)?
Some spells will be nasty however. The first time a BBEG anti-pally threatens a crit on a PC with smite up, bless weapon means you can probably kiss that PC good bye.
That being said, this exactly what the spell research rules are for, and given the cost and delayed spell access paladins/antipaladins have, it is relatively cheap/affordable to do.
Homebrew?
Somewhat. We use 3.X Materials, and Spell Compendium came to mind.
We're playing a WotW campaign, about 2/3 through the 2nd book, and we're using adjusted Weapons of Legacy rules. For my Legacy Item, I am using a +1 Mithril Full Plate.
Since we're Lawful Evil, we're obviously restricted from using Good-Aligned items or spells and the such. However, one spell from Spell Compendium (Shield of Warding) caught my eye for a constant high-level power. The issue I have with it is that it's good-aligned and it provides a Sacred Bonus to AC and Reflex Saves with the shield equipped (I use a Buckler with my two-handed weapon, GM allowed it).
Of course, because it's a Good spell doesn't mean that it can't be reworked to serve as an Evil spell. The intent as I see it is to serve a means to protect the target with enhanced force, making their shield that much more powerful. As far as I can tell, there isn't much reason for there to be an alignment restriction because of it.
Pertaining to my in-game example to the question I pose, would it be game-breaking to simply adjust the spell descriptor to Evil and adjust the bonus type from Sacred to Profane?
Of course, my question doesn't spread to simply my example (though is a reason why I ask the question); there are some other spells, even in Pathfinder books, where such a situation could arise, and is a question I would like the answer of in those situations as well.