Graham gave a link to the Add-In in his first response. The link to download it is at the bottom of the page. http://www.gmayor.com/BookmarkandVariableEditor.htm
You should read the page before downloading.

There are actually two Add-Ins in the download. I believe you want the one with Content Controls in the title. Once a content control is entered into the document as a mapped content control, you can copy and paste it elsewhere in the document. Changes to one will change all. This may take a little study to get it to work for you but is worth the time.

As Graham initially suggested, a UserForm will do what you want, but it requires vba programming. A Userform would give more options. The userform usually relates to bookmarks in the document; Graham's Add-In is useful for manipulating bookmarks as well.

• Create a Simple Userform
• Create & Employ a Userform