The President is not capable of appointing members to the military unilaterally. Congress has sole power "To raise and support Armies" and "To provide and maintain a Navy." The President's role in accessions under title 10 exists only because Congress put it there.

There are 2 million people in the military. All the president would need to do is find a handful of existing personnel and organize them. He doesn't need to "raise" or "provide" anyone.

This is exactly how Trump organized the legislative coup within the White House. He went through the ranks of the DOJ to find someone who would draft a letter to send to all the states implying that fraud had been found (a lie) and DOJ was investigating (also a lie). No one at the DOJ would do this except for Jeffry Clark, a low ranking official who was promised the role of AG if he were to carry out Trump's scheme.