Below is the Multires 3 level in object mode.
However, in edit mode, vertices, edges, and faces are displayed as Multires 0 levels.
(But the actual Multires is still 3.)
When changing to edit mode, the object is displayed as level 0, so level 3 vertices, edges, and faces cannot be edited.
Is there a way to display Multires level vertices, edges, and faces as they are in edit mode?
No.
You can display effect of levels for a Subdivision Surface modifier, in edit mode.
But Multires level support is just for sculpt mode.
So, can’t I convert the already created Multires into a Subdivision Surface at that level?
This is because the structure of the face division of Multires and Subdivision Surface is basically the same, but if I remove Multires from the current object and add Subdivision Surface, the shape of the object is slightly different.
(Since it’s a human face, even a small change is important.)
Subdivision Surface modifier does not contain a level of displacement of vertices like multires does. It uniformly subdivides and smooths the basemesh.
That is because it contains data for each level that multires modifier is not editable in edit mode where only basemesh is supported.
So, you can try to modify desired level in Sculpt mode.
Or you can
That should transfer modification done on copy to corresponding level of multires modifier.
Oh, Blender had a similar function to Zbrush’s projection.
With the process you advised, I think I can do what I intended.
Thank you for a detailed description. 
