Here we have four occurrences of requisite. The first three cases are extant in 𝓞; the fourth is not. In the three extant cases, Oliver Cowdery initially wrote the word as requisites; then in every case he immediately corrected requisites to requisite by erasing the final s. There are two other occurrences of requisite in the Book of Mormon text (in Mosiah 4:27 and Alma 61:12); the original manuscript is not extant in these two instances—or at least sufficiently extant to determine if requisites initially occurred in 𝓞. In the transcript of 𝓞 for Alma 41:3 and Alma 61:12, I presumed that Oliver Cowdery wrote requisites initially, then erased the final s. Here in Alma 41:2–3, the evidence suggests that the tendency to incorrectly add the s to requisite was probably Oliver Cowdery’s, given that when he copied the first example in Alma 41:2 from 𝓞 into 𝓟, he once more wrote requisites, and this time he did not erase the final s.
For all six instances of requisite in the text, the word acts as a predicate adjective, never as a noun, which means that the plural noun form requisites is quite unacceptable in these six cases.
But independently of the Book of Mormon, the more frequent form for the word, as a noun, is the plural requisites, not the singular requisite. For example, the Oxford English Dictionary under the noun requisite lists five citations, dating from 1602 through 1880, and every one of these citations is in the plural. It appears that the plural noun form requisites interfered with Oliver Cowdery’s ability to take down Joseph Smith’s dictation of the adjective requisite, and even once when Oliver copied the adjective from 𝓞 into 𝓟.
Summary: Maintain in Alma 41:2–3 and elsewhere in the text the non-s form for requisite; Oliver Cowdery apparently had difficulty with this word and tended to write it incorrectly as requisites.