In standard English, we expect the subjunctive were here in Alma 29:7 since the that-clause is contrary to fact. Of course, in colloquial English, was occurs in such clauses. In this instance, it appears that Oliver Cowdery initially wrote “that I were an angel” in 𝓞, but then he corrected the were to was by crossing out the were and supralinearly inserting the nonstandard was. The crossedout were is not extant in 𝓞, but the last half of the supralinear was is extant. There is no change in the level of ink flow for the extant as of was, so the correction appears to be virtually immediate. It is clear that the intended reading in the original manuscript is “that I was an angel”. The 1920 LDS edition changed the was to were, but the RLDS text has retained the original was. The critical text will restore the nonstandard was. For further discussion of was versus were in the original text, see under subjunctive and under mood in volume 3.
Summary: Restore the indicative was in Alma 29:7, the corrected reading in 𝓞 (“why should I desire that I was an angel”).