As discussed under Mosiah 10:14, Oliver Cowdery sometimes corrected nonstandard was to were, but apparently only when the actual text read that way. There isn’t much evidence that he consciously emended nonstandard was to were. Here in Alma 46:4, he initially wrote was in 𝓞, but then he soon crossed out the was and supralinearly inserted the correct were. The supralinearly were is written with slightly heavier ink flow, while the crossout and insert mark have somewhat heavier ink flow. Oliver probably made the correction here when he read the text back to Joseph Smith, although the possibility remains that Oliver was prompted by the preceding were (“which were wroth”) to emend the following was to were. For a similar example of was corrected to were in the manuscripts, see the nearby discussion under Alma 46:33.
Summary: Maintain the plural were in Alma 46:4, Oliver Cowdery’s corrected reading in 𝓞: “and those people which were wroth were also desirous that he should be their king”.