Here in 𝓟, Oliver Cowdery initially wrote “according to the word of the Lord God”; then later, most likely when proofing 𝓟 against 𝓞, Oliver crossed out the words the Lord (giving “according to the word of God”). The ink flow for the crossout is considerably heavier but probably does not represent editing since there are two similar corrections in heavier ink flow on the next page of 𝓟 and these two corrections (both supralinear insertions) are undoubtedly the result of proofing 𝓟 against 𝓞. For discussion of these two corrections, see the discussion under Omni 1:6.
Both expressions, “the word of the Lord” and “the word of God”, are found in the original Book of Mormon text, with 30 occurrences of the first and at least 90 of the second (the number depending on the analysis). Although there are no occurrences of the fuller expression “the word of the Lord God” in the Book of Mormon text, there are many examples of “the Lord God” (112 occurrences). Of these 112, only two read “of the Lord God”, and in both of these cases, God is postmodified by an adjective:
It is highly unlikely that Oliver Cowdery would have been aware of this minor restriction on the use of “of the Lord God” (namely, its adjectival postmodification). Thus there would have been little motivation for Oliver to have deleted the Lord from the phrase “of the Lord God” in Jarom 1:10— except that the text didn’t read that way in 𝓞. Oliver’s correction here appears to have restored the original reading as found in 𝓞 (no longer extant here).
Summary: Accept Oliver Cowdery’s corrected reading in Jarom 1:10: “according to the word of God”.