Blood of Fiends pages 18-23 are PFS allowable presuming you hold the Tiefling Boon.
The Rakshasa-Spawn trades the standard tiefling ability mods for +2 Dex +2 Cha -2 Wis, trades the Skill modifiers for Disguise and Sense Motive, and trades the spell like ability Darkness for Detect Thoughts. Those things that aren't overwritten or specifically listed as being part of the exchange, (Fiendish Resistance, Fiendish Sorcery, and Languages), remain unchanged.
This looks straight forward to me. Is there something I'm missing?