The 1837 edition introduced the reading righteous. This may reflect editing by Joseph Smith or perhaps an error on the part of the 1837 typesetter. Speakers of English expect “his paths are righteous”, and that may be the reason the text was changed, whether intentionally or accidentally, here in 2 Nephi 9:41. The 1908 RLDS edition restored the reading of the printer’s manuscript (“his paths are righteousness”).
The King James Bible refers to both “the paths of righteousness” (Psalm 23:3) and “the paths of the righteous” (Proverbs 2:20). If we expand our search to include way(s) as well as path(s), we find that the Book of Mormon has similar examples with both righteousness and righteous:
righteousness
righteous
But in all of these examples, the word righteousness or righteous is found in a prepositional phrase headed by of. In 2 Nephi 9:41, the word righteousness (or righteous) is a subject complement: “his paths are righteous(ness)”. Although there are no other examples that use path(s) in this manner, there is one with way(s):
This example clearly shows that the original usage in 2 Nephi 9:41 (“his paths are righteousness”) is fully acceptable.
Summary: Maintain righteousness, the reading of the earliest text in 2 Nephi 9:41 (“his paths are righteousness”); the expression “his ways are righteousness” in 2 Nephi 1:19 supports righteousness as the correct reading in 2 Nephi 9:41.