[BenKenobi]

Reynold's confirmed that the Federal government had the authority to require Utah to conform to the common law definition of marriage between one man and one woman. Again, the definition of marriage doesn't change in your example. Just the specifics. States have the authority to change their ages of majority. Redefining marriage, in changing the one man, one woman formula, is not permitted. It's never been a state right to redefine, else Utah's polygamy ban would have been thrown out by the SCOTUS. Instead, it was affirmed by appealing to the English common law traditions well older than the constitution.

[OldDeckHand]

"Reynold's confirmed that the Federal government had the authority to require Utah to conform to the common law definition of marriage between one man and one woman."

No, it didn't. That wasn't the question that was put to the test in Reynolds. I've already cited for you the relevant the section of Reynolds, but, it appears you've chosen to ignore it. I'm not sure if you don't understand how to read legal opinions, or what. From Oyez, on this very matter...

Facts of the Case: George Reynolds, secretary to Mormon Church leader Brigham Young, challenged the federal anti-bigamy statute. Reynolds was convicted in a Utah territorial district court. His conviction was affirmed by the Utah territorial supreme court.

Question: Does the federal anti-bigamy statute violate the First Amendment's free exercise clause because plural marriage is part of religious practice?

Conclusion: No. Chief Justice Morrison R. Waite, writing for a unanimous court, held that the statute can punish criminal activity without regard to religious belief. The First Amendment protected religious belief, but it did not protect religious practices that were judged to be criminal such as bigamy. Those who practice polygamy could no more be exempt from the law than those who may wish to practice human sacrifice as part of their religious belief.