So…
As I said - I was not able to solve the soduko itself.
BUT - each letter in the final answer is derived from a single digit of 1…9 plus some given number. This means that each letter only has a range of 9 specific letters. For example, the first letter is the (alpha-converted) top-left digit + 2. So the minimal letter is ‘C’ (1+2 = 3 → C) and the maximal letter is ‘K’ (9+2 = 11 → K).
Using this insight it’s easy to construct the following regular expression for the code word:
^[c..k][a..i][e..m][g..o][h..p][d..l][c..k][a..i][q..y]$
When running this regex on an English dictionary, you get very few hits, and only one of them makes sense. And this is indeed the solution.