Ahriman's obedience reward states:
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Obedience: While praying to Ahriman, destroy something
of monetary or sentimental value to another person,
preferably in front of someone who feels a strong emotional
connection toward it. Alternatively, voluntarily take 1 point
of Constitution damage while chanting praises to Ahriman
and flagellating yourself with a barbed lash. After performing
this obedience, your true alignment is masked from
detection. Each time you perform this obedience, you select
an alignment that you wish to detect as. Once chosen, this
alignment can’t be changed until you perform this obedience
again or 24 hours pass. The masked alignment can trick items
and magic that require a particular alignment. For example,
a neutral evil follower can make her alignment appear to be
lawful good, which would allow her to safely pass beyond a
glyph of warding keyed to lawful good.
______
My question is: I'm planning to make an Antipaladin, follower of Ahriman. After I take the Fiendish Obedience feat at lv3 and perform the obedience daily (with the barbed lash since the other condition is way too situational), does that mean that effects like "Smite Evil" no longer work on me if I make my alignment to become, say, True Neutral or Neutral Good? Also magics like Holy Word and so on would lose their effectiveness completely?
Smite Evil is magic that requires a particular alignment, so yeah, you can really screw a Paladin with this.