Indeed, Su Changkong was planning to sneak into the Dafeng Iron Cavalry's army camp and hide for a year or a year and a half to evade the possible pursuit of the Mu Family. Among the skills he mastered was his old trade: forging!
The Dafeng Iron Cavalry had 400,000 men, all needing armor, weapons, bows and arrows which required the work of blacksmiths. Therefore, blending in with the military as a common blacksmith would not draw attention, nor would he need to worry about giving himself away, after all, he was truly skilled in forging!
Thus, Su Changkong decided to use this method to blend into the densely populated army camp, return to his old trade, hide out for a year or so, and wait for the Wood Snake Seal to fade away with time. At that point, he could find an excuse like needing to care for sick parents to resign and leave.