So, to answer seriously: if it’s an explicit presidential power he gets total personal immunity, although the office can still be restricted. If it’s an official act, he’s presumed to have personal immunity unless the prosecutor can argue that there’s no way that not having immunity could get in the way of doing the job of president, and they’re not allowed to use motivation to make the case.
The president isn’t given the explicit power to reform the courts.
He’s given explicit power to command the armed forces, but the rules of the armed forces are decided by Congress.
So it’s a question arguing how “the president can’t kill members of the judiciary” doesn’t hinder the power of the executive branch without referencing why the president is killing them.