And they also took of the firstlings of their flocks, that they might offer sacrifice and burnt offerings according to the law of Moses (Mosiah 2:3)
Some critics of the Book of Mormon (e.g., M.T. Lamb; the Tanners) have argued that this passage shows that the author of the Book of Mormon “blundered” with their (purportedly, lack of) understanding of the Law of Moses as, they argue, the “firstlings of the flock” were never sacrificed as “burnt offering.” Such as ably responded to by Matthew P. Roper:
Notwithstanding, there is Old Testament precedent for alternations to the sacrificial system if and when needed. In 2 Chron 30:13-22, we read the following:
A great crowd assembled at Jerusalem to keep the Feast of Unleavened Bread in the second month, a very great congregation. They set to and removed the altars that were in Jerusalem, and they removed all the incense stands and threw them into Wadi Kidron. They slaughtered the paschal sacrifice on the fourteenth of the second month. The priests and Levites were ashamed, and they sanctified themselves and brought burnt offerings to the House of the Lord. They took their stations, as was their rule according to the Teaching of Moses, man of God. The priests dashed the blood which they received from the Levites.7 Since many in the congregation had not sanctified themselves, the Levites were in charge of slaughtering the paschal sacrifice for everyone who was not clean, so as to consecrate them to the Lord. For most of the people -- many from Ephraim and Manasseh, Issachar and Zebulun -- had not purified themselves, yet they ate the paschal sacrifice in violation of what was written. Hezekiah prayed for them, saying, "The good Lord will provide atonement for everyone who set his mind on worshiping God, the Lord God of his fathers, even if he is not purified for the sanctuary." The Lord heard Hezekiah and healed the people. The Israelites who were in Jerusalem kept the Feast of Unleavened Bread seven days, with great rejoicing, the Levites and the priests praising the Lord daily with powerful instruments for the Lord. Hezekiah persuaded all the Levites who performed skillfully for the LORD to spend the seven days of the festival making offerings of well-being, and confessing to the Lord God of their fathers. (1985 JPS Tanakh)
Commenting on this pericope, Jacob B. Myers wrote:
Of course the writer’s enthusiasm is evident through his reference to the very large congregation. A further reformation took place, this time in the city from which all foreign accoutrements of worship were removed and cast into the refuse place in the Kidron Valley. The response of the people inspired the priests and Levites to consecrate themselves so that they occupied their stations for the service. Hence they could also step in to slay the Passover lambs for those who would not meet ritual prescriptions. (This was probably a misunderstanding, as Rudolph, p. 301, thinks, as according to the law [Exod xii 6; Deut xvi 6] the family heads were to slay the lambs. The Levites probably did act for those from Israel who were not ritually capable of doing so.) The whole combination of festivities-festival of unleavened bread, Passover, and peace offerings—continued for a full seven days after which the Levites were congratulated by the king—another indication of the esteem in which they were held by the Chronicler. The story probably had some homiletic application for the writer. (Jacob M. Myers, II Chronicles: A New Translation with Introduction and Commentary [AB 13; New York: Doubleday, 1965], 178-79, emphasis added)
In other words, the priests and Levites altered the prescriptions of the sacrificial system, accommodating such to the needs of the time, and such actions were praised, not condemned, by the Chronicler. One could argue, then, that just as the Sabbath was made for man, not man made for the Sabbath, in some instances at least, the sacrificial system was made for man, not man for the sacrificial system, similar to the variability, as noted by Roper, in antiquity of the firstlings of the flock and the olah (burnt sacrifice).