For the 1837 edition, Joseph Smith eliminated what could be considered an intrusive and before the second if-clause. This second if-clause (“if ye do this”) summarizes the content of the first (and rather long) if-clause. Given the extra and, the first if-clause is incomplete and appears fragmented. Nonetheless, there is at least one other example in the text where an initial long if-clause is followed by a shorter if-clause that restates the first if-clause and is at the same time separated from that first if-clause by an and:
In this instance, we have a long intervening parenthetical statement (“and God will shew unto you with power and great glory at the last day that they are true”), which leads to starting over with a summarizing if-clause, yet with an intervening and, just like originally in Mosiah 7:33. Consequently, we should probably assume that the extra and ’s in Mosiah 7:33 and Moroni 7:35 are not errors but instead are actually intended.
Summary: Restore the and that originally preceded the summarizing if-clause in Mosiah 7:33; for a similar example, which has never been edited, see Moroni 7:35.