Here in the printer’s manuscript, Oliver Cowdery initially wrote “by the hand of God”, which is what we expect. Elsewhere in the text there are four instances of the expected phraseology:
Yet here in 3 Nephi 3:2, the original manuscript undoubtedly read “by the hand of a God” since the 1830 edition reads this way (as does the corrected reading in 𝓟). Most likely Oliver added theindefinite article in 𝓟 when he later proofed 𝓟 against 𝓞 (the supralinearly inserted a is written with a duller quill and with somewhat heavier ink flow).
Beginning with the 1920 edition, the LDS text has spelled God in this verse without capitalization, as god. This makes sense since the reference here is generic. As discussed under Mormon 9:10, the critical text will accept the spelling god without capitalization in generic cases. For further discussion of capitalization in reference to deity, see under 1 Nephi 1:9.
Summary: Accept in 3 Nephi 3:2 the indefinite article a before god as well as the lowercase spelling for this generic reference to a god.