Oliver Cowdery’s deletion of & in the printer’s manuscript is definitely an immediate correction. First, the level of ink flow is the same. Second, Oliver first tried to overwrite the ampersand with he, but he only overwrote with the first half of the initial h, then simply crossed out the whole partially corrected ampersand and wrote the he inline immediately to the right of the crossout. The original manuscript is not extant here, but it seems highly probable that 𝓞 didn’t have an ampersand. Oliver may have expected an additional and simply because and (written as &) had already occurred twice in the immediately preceding clause (written in 𝓟 as “& because that he had fallen from heaven & had became miserable forever”).
Summary: Accept Oliver Cowdery’s crossout of the additional ampersand in 2 Nephi 2:18; the nature of the crossout argues that and was not in the original manuscript.