Sun and Moon Seeker

Although Ace was in someone else's body, the Sword Intent and his other Law comprehensions were something that had etched into his very being. So, unless someone can reset his mind, these things will never go away. 

The moment Ace used the newly developed, overbearing Eternal Thief's Sword Style with a mortal body, the body was bound not to last more than a few seconds.

However, Ace didn't care as he knew the trial was to kill that thing. It doesn't matter how he killed it. So, despite this suicidal move, he should be fine. Even if he failed, at least he would come prepared next time. 

As for the matter of the Union Leader watching, he had a very good excuse for his month's study as well as he could also lie about this body having such an ability already, like the ability to use Qi without refining.