The original manuscript is extant here for part of this verse, and it provides strong evidence that the 1830 edition was set from 𝓞 for this part of the text. In 𝓞 itself, Oliver Cowdery started to write the word my at the end of the line. But only the initial m fit, and he decided not to hyphenate this two-letter word; instead he wrote the whole my at the beginning of the next line. Accordingly, he erased the line-final m that he had initially written in 𝓞, but he did not cross it out. At first glance, his erased m looks like in, and this is precisely what the 1830 compositor initially set in the 1830 edition: “which is in my name”. Later, this typo was caught and an in-press change was made during the 1830 printing: the in was removed, giving the correct “which is my name”. The printer’s manuscript, also a direct copy of the original manuscript, has simply “which is my name” and was not the source for the incorrect insertion of the in in the initial typesetting of the 1830 edition. This variant does not affect the reading of the text, but it does provide further evidence that from Helaman 13:17 through Mormon the 1830 edition was set from 𝓞.
Summary: The correct text for 3 Nephi 27:5 is “which is my name”, not “which is in my name” (the initial reading for the 1830 edition).