The printer’s manuscript has the impossible word order will I set after the initial connective phrase and again. The and again here means ‘and again I say’. This expression is found explicitly at the beginning of the next verse: “and again I say : he that departeth from thee shall no more be called thy seed” (Alma 3:17). Clearly, the again in verse 16 does not modify the verb set; the text is not saying that the Lord will set a mark a second time on those who fight against Nephi and his descendants. (For the various uses of the word again in the Book of Mormon text, see the discussion under 2 Nephi 5:11.) We should also note here that the preceding verse also uses and again as a narrative connector:
The only time we have the inverted word order after the connective phrase and again is when the sentence is a yes-no question, as in Mosiah 5:14: “and again : doth a man take an ass which belongeth to his neighbor and keep him”. In this case, the inverted order is required regardless of whether and again is there or not.
Thus here in Alma 3:16 the inverted order will I set in the printer’s manuscript must be a scribal error. The 1830 typesetter switched the word order in verse 16 to the correct I will set and also set a colon after and again (just like he did in verse 15). We have no other evidence for this specific kind of error in the textual history for the Book of Mormon, although there is evidence that Oliver Cowdery occasionally switched the word order when the sentence began with an adverbial phrase:
There are no examples of scribe 2 of 𝓟 making this kind of error. Even so, the reading in 𝓟 is clearly unacceptable and must be the result of some scribal slip, either when 𝓞 was written down or when it was copied into 𝓟. The critical text will maintain the 1830 typesetter’s emendation of will I set to I will set.
Summary: Retain in Alma 3:16 the 1830 printer’s emendation of the word order from will I set to I will set (“and again : I will set a mark upon him”).