This is called “placing Biden” in a box. Until his nominees are successfully voted on in the Senate and sworn in, PDJT’s people will run the “shops”. They can, and will, slow down any changes Pedo Joe wants to make. If the Republicans maintain the Senate then it may take months for Pedo Joe to get his people in place and make the changes. This is also in anticipation that Pedo Joe will fire, on day one, all of PDJT’s secretaries, making it essential to have line of succession spelled out. Pedo Joe could just issue another EO changing PDJT’s EO’s but there will be a lot of major pushback, including potential lawsuits.
Those appointed by the President will normally leave when his term ends. When Obama was elected some really great men and women simply resigned and moved on. It had to hurt because they had all but managed the war time military. If you are appointed the president can relieve you on day one. Some are career bureaucrats, they are not so easily pushed aside. There are rules that have to be followed and that takes time.