The editing for 1 Nephi 17:46 involves replacing a that-clause with an infinitive clause. The earliest textual source (the original manuscript) reads “he can cause that rough places be made smooth and smooth places shall be broken up”. Joseph Smith probably found the lack of a finite verb in “rough places be made smooth” awkward, so he deleted the that and inserted the to (although only the second change is marked in the printer’s manuscript). A similar kind of editing is found in 1 Nephi 17:12, although here in 1 Nephi 17:46 there is a different verb (cause instead of make). In addition, restoring the original text for 1 Nephi 17:46 turns out to be more complicated.
Elsewhere the original text is about equally divided between cases where the verb cause is followed by a that-clause and by an infinitive clause (123 to 106). There are also 12 additional cases involving the that-clause where the subject of the clause appears first as the direct object right after the verb cause and is then repeated as a subject pronoun in the that-clause. In fact, such an example is found earlier in this same verse:
So elsewhere in the text there are a total of 135 (= 123 + 12) occurrences of cause followed by a that-clause. And in every one of these other cases, the that-clause has a modal verb, either should (121 times), shall (11 times), or may (3 times). (The should dominates because in most instances the verb cause is in the past tense, which consequently requires the past-tense modal should in the following that-clause.) These statistics mean that there is not one other example where the verb in the following that-clause is in the subjunctive rather than the indicative mood. In other words, there is no support elsewhere for the subjunctive phraseology of “that rough places be broken up” after the verb cause. Thus the earliest reading in 1 Nephi 17:46 is doubtful as the original text; the that-clause following cause seems to be missing its modal verb. And the following conjunct (“and smooth places shall be broken up”) suggests, of course, that the missing modal is shall. In any event, Joseph Smith’s editing is problematic here since it ends up conjoining an infinitive clause and an indicative clause (“he can cause rough places to be made smooth and smooth places shall be broken up”). To be consistent, Joseph could have changed the second clause to “and smooth places to be broken up”.
There is scribal evidence elsewhere that Oliver Cowdery sometimes dropped the modal verb shall. All of the examples involve his copying from 𝓞 into 𝓟. And in all of these cases but the first one, he caught his error:
In the last example, Oliver Cowdery initially omitted the shall in 𝓟, but shortly afterwards he supralinearly inserted it (the level of ink flow is somewhat heavier). For this part of the text, both 𝓟 and the 1830 edition are firsthand copies of 𝓞. In addition, the corresponding verse in the King James Bible has the shall (“and shall say all manner of evil against you”, in Matthew 5:11).
We should note that in each of these instances, the omitted shall is found in a dependent clause, just as it would have been in 1 Nephi 17:46. Although none of these examples show Oliver Cowdery omitting shall in the original manuscript, they do show that he has a tendency to drop this modal verb in subordinate clauses. Another difference is that in each of these six examples of scribal error, the resulting text (that is, without the shall ) is acceptable. In 1 Nephi 17:46, on the other hand, the missing shall does seem to create an awkward expression. In any event, the internal evidence from usage elsewhere in the text argues that 1 Nephi 17:46 originally read “he can cause that rough places shall be made smooth”.
Summary: In 1 Nephi 17:46, emend the text to read “he can cause that rough places shall be made smooth and smooth places shall be broken up”; there is strong internal support for proposing that the original text had shall in both of the conjoined indicative clauses.