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The attached workbook will show a message when you open it, and this is the code that does the job.
Private Sub Workbook_Open()
' 13 Jul 2018
' Note: There is a limit to the width you can use:
Const MsgWidth As Long = 45 ' number of characters
Dim Prop As String
Dim Msg As String
' Set the property
ThisWorkbook.BuiltinDocumentProperties("Author") = "Mickey Mouse"
' recover the property value
Prop = ThisWorkbook.BuiltinDocumentProperties("Author")
' construct the message
Msg = String(MsgWidth, "+") & _
String(2, vbCr) & String(28, " ") & _
"This workbook was created by" & _
String(2, vbCr) & String(40, " ") & _
Prop & String(2, vbCr) & _
String(MsgWidth, "+")
MsgBox Msg, vbInformation Or vbOKOnly, "Important Information"
End Sub
You will find the code in the ThisWorkbook module. Press Alt+F11 to open the VB Editor and navigate to the code module there. Observe that the workbook is macro-enabled. You will have a demonstration of why your idea is only of limited feasibility with this test.
Macros can be dangerous to your computer. Therefore Excel disables them by default. When you open the attached workbook you may be prompted to confirm that you want to allow macros to run. In fact, your security settings may even disable this question. Therefore the message may not run for everyone. If it doesn't run for you check your macro security settings.
Second, the attached workbook has all personal information removed from it. That is the standard for published workbooks, and it includes the author's name. I was unable to publish a workbook here with the Author's property set. Hence the lines to set the author's name in the first place.
' Set the property
ThisWorkbook.BuiltinDocumentProperties("Author") = "Mickey Mouse"
When you deploy this macro in your workbook the "Author" property should be set manually and these lines of code deleted from the macro. You can just enter an apostroph at the beginning of the line to make it ineffective.
Of course, anyone can set the Author property and thereby change the message. You may use the above code to undo any change the user might make and reinstate the author's name. Or you might use this line of code to bypass the built-in property altogether. Change the existing line of code Prop = ThisWorkbook.BuiltinDocumentProperties("Author") to Prop = "Mickey Mouse" and that name will appear in the message.
I have created a rough design for the message which you can modify, of course. Modify the total width Const MsgWidth As Long = 45. Note that the maximum width Excel allows depends upon the character you choose. I chose "+" and for that character 45 is max on my machine and my settings for Excel.
String(MsgWidth, "+") creates a string of [45] repetitions of "+"
String(2, vbCr) & String(28, " ") inserts 2 x [Enter] followed by 28 spaces.
Observe the ampersand between the expressions to concatenate them into one string and the trailing underscore, preceded by a space, to write a concatenation in several lines of code.
Note that a more elaborate message would be possible by showing a Userform instead of a message box. However, the startup limitations are caused by VBA and can't be avoided. The applicable principle is that the supplier of the workbook can't take control of the recipient's computer for better or for worse. The recipient has to be allowed to decide which code he wants to allow to run on his machine.