Try changing the Name value under Edit - Preferences - Identity.
You need to disable the "Always use Log-in name for Author Name".
Create any comment.
Select the comment.
Use right mouse click to select "Prperties".
Change properties of the comment, especially the Author's Name and click "OK".
Select comment and use right mouse click to select "Set as Default".
Test by creating a new comment.
That only changes the name used as the Author property of the stamp annotation, not the name used in the stamp itself, I believe.
Correct, the name that shows up on the dynamic stamp is taken from the identity information.