Here the earliest text reads “a respecter to persons”. The 1841 British edition replaced the to with the more expected of, but the 1849 LDS edition restored the earlier preposition. Similarly, the 1874 RLDS edition has of rather than to; the 1908 RLDS edition restored the correct to. Under Alma 1:30, I thoroughly discuss the variation between to and of in this phrase as well as in related phrases using respect or respects; in particular, Alma 1:30 originally read “having no respects to persons”. For each case involving respect(s) or respecter, the critical text will follow the earliest text in choosing between the prepositions to and of, thus to here in Moroni 8:12.
Summary: Maintain the original preposition to in Moroni 8:12 (“a respecter to persons”); similar usage is found in Alma 1:30 (“having no respects to persons”).