Matthew 5:18 (King James Bible) one jot or one tittle shall in no wise pass from the law till all be fulfilled
As discussed under 2 Nephi 23:17, the original text has instances in negative clauses of noun phrases parenthetically conjoined to a preceding noun phrase by the conjunction nor, as in this other example dealing with jots and tittles from earlier in 3 Nephi:
In that case, the nor was emended to or in the 1920 LDS edition and in the 1953 RLDS edition. But here in 3 Nephi 12:18, the nor has not been emended to or (which is the conjunction that the corresponding King James reading has). The critical text will, of course, retain this original use of nor since usage elsewhere in the Book of Mormon text supports it.
Summary: Accept the use of nor in 3 Nephi 12:18, the reading of all the textual sources; although Matthew 5:18 has or, usage elsewhere in the Book of Mormon allows nor for this kind of negative expression.