If he could, HE SHOULDN’T. VERY bad idea.
While it would be allowable, politically, it would create a political firestorm that makes the current one look like a candle.
Why? It’s Constitutional per Article 2 Section 2, although the commissions expire at the end of the next session. Pretending that a valid part of the Constitution is a “very bad idea” plays into the liberals’ hands.
Now if the Senate refuses to adjourn, it becomes evident what they would be thinking.
Why not? Whose side are you on? The executive function is vested in one man alone, Donald Trump. Within his Constitutional powers, nobody can tell him no.