Steven H was telling us:
Steven H nous racontait que :

Have you looked at the online help for the code I suggested
(CustomDocumentProperties)?

CustomDocumentProperties Property

Returns a DocumentProperties collection that represents all the custom
document properties for the specified document.

expression.CustomDocumentProperties
expression    Required. An expression that returns one of the objects in the
Applies To list.

Remarks
Use the BuiltInDocumentProperties property to return the collection of
built-in document properties.

For information about returning a single member of a collection, see
Returning an Object from a Collection.

Example
This example inserts a list of custom built-in properties at the end of the
active document.

Set myRange = ActiveDocument.Content
myRange.Collapse Direction:=wdCollapseEnd
For Each prop In ActiveDocument.CustomDocumentProperties
   With myRange
       .InsertParagraphAfter
       .InsertAfter prop.Name & "= "
       .InsertAfter prop.Value
   End With
Next

This example adds a custom built-in property to Sales.doc.

thename = InputBox("Please type your name", "Name")
Documents("Sales.doc").CustomDocumentProperties.Add _
   Name:="YourName", LinkToContent:=False, Value:=thename, _
   Type:=msoPropertyTypeString

So, if you can create it, you can certainly change the value, as exemplified
in the following:

Dim strName As String

strName = InputBox("Please type your name", "Name")

With ActiveDocument
   .CustomDocumentProperties.Add "YourName", False, _
       msoPropertyTypeString, strName
   MsgBox .CustomDocumentProperties("YourName").Value

   .CustomDocumentProperties("YourName").Value = "New Name"
   MsgBox .CustomDocumentProperties("YourName").Value
End With

VBA has a special function that detects the user's idiocy level, and
disables application functionality accordingly.