As @crinrict says, it wouldn't make sense if it worked for last names but not for first names. Also, the TS4 team really looked into Polynesian cultures and languages to not mess things up, so I'm pretty sure that they know that they should use apostrophes, not accents. (Sulani is based on Polynesian cultures.)
Anyway, I tried it with both acute accent (´) and grave accent (`) in the cheat code, just to make sure, and the cheat returns "Sim not found" if I write Paka´a Uha or Paka`a Uha, and the symbol in CAS really looks like an apostrophe anyway.
Enable cheats. Enter cas.fulledit mode cheat. Change the symbol to an apostrophe in the name of the island person you want to change. Then save. When you type in the relationship cheat it will work this time. I just tried it.
Would it work to type quotation marks around the name when entering the cheat? That's what one has to do for two-word first names.
Like this: "Silver Moon" Thompson
