Here the 1841 British edition replaced the preposition to with of, which the LDS text followed until the 1920 edition, when the original to was restored. Note that the previous participial clause also has the preposition to (“being an enemy to God”). As noted in the discussion under Mosiah 3:19, the original Book of Mormon text has examples of both “an enemy to God” (four times) and “an enemy unto God” (one time) but none of “an enemy of God”; on the other hand, if the article is the, we get “the enemy of God” (one time). In each of these cases, we allow the earliest textual sources to determine the reading.
Summary: Maintain in Mosiah 16:5 the two occurrences of the preposition to in the phrase “an enemy to God”, the reading of the earliest text for this passage.