If you use a mnemonic editor, you can undo 2 character levels’ worth of decisions about which class levels you took, which feats you selected, how you applied any level-based increases to ability scores, how you assigned new skill ranks, and so on. All decisions you made as a result of advancing over the previous 2 character levels you gained are undone. You then make new selections, including new class levels, feats, skills, and the like, as if you had regained the 2 missing character levels. Go through the normal process of advancing your character through each of these 2 levels.
A copaxi gradually reshapes its body and neural networks to overcome new challenges. Each time a copaxi gains a level, it can retrain all the choices of one previous character level, as though it had used a mnemonic editor. They must have qualified for any new selections at the retrained level.
Mnemonic editor retraining is known to be restricted to the previous two character levels.Is the Copaxi racial ability retraining also limited to the previous level, or can I use it to retrain any level I have previously taken?
Example: 4th-level Copaxi has taken levels in 1) Solarian 2) Envoy 3) Mystic 4) Soldier. Can the character retrain any one of those when he reaches level 5, or just the soldier level?
My own reading of the rules would lean on the side of "any previous level" on the basis that the ability allows me to retrain "one previous character level" instead of "the previous character level", and the part about "as a mnemonic editor" refers to what can be retrained. I have been wrong before and I shall be wrong again, however.
Assume that bookkeeping is not the issue; in case of mnemonic editors we should already track the order in which levels are taken for a multiclass character, and including detailed information about the level-up process is a few extra words.
While houserules are a decent solution to everything, I would prefer an answer that would be valid for Starfinder Society play. If the question should be made on those boards, please flag the thread for moving.