Here in the original manuscript, Oliver Cowdery initially wrote even somuch, which he soon corrected to even insomuch by supralinearly inserting the in. The ink level for the correcting in is only slightly heavier, which suggests that Oliver’s correction occurred after he redipped his quill. Elsewhere the text has four examples of even so much and one more of even insomuch:
Since either reading is possible, the critical text will accept the corrected reading in Alma 24:2 (“even insomuch that they began to rebel against their king”).
The original spelling of so much here in Alma 24:2 as somuch (that is, as one word) should not be interpreted as evidence for insomuch and against so much as the original reading, mainly because Oliver Cowdery sometimes spelled legitimate occurrences of so much as one word (1 time in 𝓞, 3 times in 𝓟). In fact, insomuch is also often written by Oliver with spaces: in somuch (2 times in 𝓟), inso much (1 time in 𝓞, 9 times in 𝓟), and in so much (2 times in 𝓟). Thus the spelling somuch (with no space between so and much) plays no role whatsoever in Alma 24:2 (or anywhere else) in determining whether the text should read insomuch or so much.
Summary: Accept in Alma 24:2 Oliver Cowdery’s corrected reading in 𝓞: “even insomuch that they began to rebel against their king”.