Given that you are attracted to autonumbering as suggested, the following macros will address that. The first replaces your numbered items with Sequence fields. The second will add a number using the same sequence and update the sequence to reflect the addition.
Code:
Sub ReplaceNumbers()
Dim oRng As Range
ActiveWindow.ActivePane.View.ShowFieldCodes = True
Set oRng = ActiveDocument.Range
With oRng.Find
Do While .Execute(findText:="\[[0-9]{1,}\]", _
MatchWildcards:=True, _
Wrap:=wdFindStop, _
Forward:=True) = True
oRng.Fields.Add oRng, wdFieldSequence, "List\# ""'['0']'""", False
oRng.Collapse 0
Loop
End With
ActiveWindow.ActivePane.View.ShowFieldCodes = False
lbl_Exit:
Set oRng = Nothing
Exit Sub
End Sub
Sub AddNumber()
Dim oRng As Range
Dim oField As Field
ActiveWindow.ActivePane.View.ShowFieldCodes = True
Set oRng = Selection.Range
oRng.Fields.Add oRng, wdFieldSequence, "List\# ""'['0']'""", False
oRng.Collapse 0
ActiveWindow.ActivePane.View.ShowFieldCodes = False
For Each oRng In ActiveDocument.StoryRanges
For Each oField In oRng.Fields
oField.Update
Next oField
Next oRng
lbl_Exit:
Set oRng = Nothing
Set oField = Nothing
Exit Sub
End Sub