Is it somehow a possibility in the rules? Question that's come up because of campaign using Race Building with enough points to have Undead races. Would it have to be house ruled?
Since they're not required to be evil, the problem would come up with undead Clerics and Paladins.
There is a spell(Life Channel?) with a similar affect, but if you want something that is always on then it will require a houserule.
You could use 'undead' that are not really undead, like incutilis-driven bodies, or yellow musk zombies, or other possibilities...
Animated "skeletons" crafted from greenwood?
There is a 4th level spell in the Undead Slayer's Handbook reverses negative energy affinity (into positive).
Positive Energy Affinity for undead makes as much sense as Negative Energy Affinity for living creatures.
I say, swap the polarity of the existing feat, and run with it.
And let's kill the 'undead are always evil' trope while we're doing so.
I'm all for this, the problem being that it's not a feat but a racial trait, and a weakness at that.
Part of the flip should be moving it out of the weakness category (probably to either other or magic) and switch it to a +1 cost (maybe even +2)
that being said I'm all for some good undead