The regulative principle is used to forbid traditional customs like Christmas. One of the prooftexts for the regulative principle is the cautionary tale of Nadab and Abihu (Lev 10:1-2; Num 3:4; 26:61).
What they did wrong depends in part on which version you quote. The NIV says "contrary to his command" whereas the ESV (and NASB) says "which he had not commanded".
There's an elementary difference between doing something that God has not commanded and doing something contrary to what God has commanded.
There are, however, some other textual clues:
i) The fact that they resorted to "unauthorized fire" suggests that they violated Lev 16:12. Instead of getting kosher coals from the high altar, they took coals from some other source. Maybe a campfire.
The significance of coals from the high alter derives from the fact that God himself ignited the altar. So that would be supernatural fire which signifies God himself (God is light), rather than a human fire.
In that event, their transgression lay not in doing something that God hadn't commanded, but in disobeying something that God had commanded.
ii) Another possibility is that they usurped the role of the high priest by entering the inner sanctum. If so, their transgression lay not in doing something that God hadn't prescribed, but in something that God had proscribed.
It's possible that they were guilty of both. And there are other explanations, although the evidence is more tenuous.
In any case, I don't see any exegetical evidence that they were punished for merely doing something not commanded, but for doing something they were commanded not to do. On the face of it, prootexting the regulative principle from the fate of Nadab and Abihu is a bait-n-switch. Note the slippage from what is not commanded to what is prohibited, as if those are equivalent concepts.
iii) The accounts of what they did wrong are sketchy, but the gist of it seems to be that they brought something profane into contact with something holy. In the Mosaic cultus, there were ritually pure inanimate objects. Holy furniture, holy utensils, holy vestments, holy places, &c. Mingling what was unholy with what was holy, in this sense, was forbidden.
However, we don't have holy inanimate objects under the new covenant. We don't have the purity codes and kosher laws.
iv) In addition, the Puritan position reduces to the notion that we should only celebrate Jesus once every 7 days. Not celebrate him the other 6 days of the week. But surely Christians should celebrate Jesus all the time.