You can add additional field to your page type named 'Byline'. This field will be editable on Form tab of each page. Then you can include some viewer web part like Document Viewer or repeater. Then configure Path like './' (it means to display information for current page). And add transformation where you cat do something like <%# Eval("Byline") %>
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Or alternative way is to use static html web part and add macro there {%CurrentDocument.Byline|(identity)GlobalAdministrator%}
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