Install & Uninstall add-ins with a VB 6.0-based approach

Option Explicit

Private Sub Uninstall_Click()
Dim objRootKey As RegKey
Dim objStartKey As RegKey
Dim objValue As RegValue
Dim stName As String
    
Const stSubRoot1 As String = "Software\Microsoft\Office\10.0\Excel\Options"
Const stSubRoot2 As String = "Software\Microsoft\Office\10.0\Excel\Add-in Manager"
Const stAddin As String = "C:\DDE\Test.xla"

'Get the predefined root-key.
Set objRootKey = RegKeyFromHKey(HKEY_CURRENT_USER)

'Parse the subkey.
Set objStartKey = objRootKey.ParseKeyName(stSubRoot1)

'Loop through the subkeys Options values to obtain the correct OPEN-name
'for the add-in.
'This is applicable when add-ins are activated.
For Each objValue In objStartKey.Values
    If objValue.Name Like "OPEN*" Then
        If objValue.Value = """" & stAddin & """" Or _
           objValue.Value = stAddin Then
            stName = objValue.Name
            Exit For
        End If
    End If
Next objValue

'Loop through the subkey Add-in Manager names to obtain the correct name.
'This is applicable when add-ins are deactivated.
If Not stName = "" Then
    Set objStartKey = objRootKey.ParseKeyName(stSubRoot2)
    For Each objValue In objStartKey.Values
        If objValue.Name = stAddin Then
            stName = objValue.Name
            Exit For
        End If
    Next objValue
End If

If stName = "" Then
    MsgBox "Not able to locate the add-in " & stAddin & "!", vbCritical
Else
    'Remove the add-in.
    objStartKey.Values.Remove stName
End If
  
'Release objects from memory.
Set objValue = Nothing
Set objStartKey = Nothing
Set objRootKey = Nothing
    
End Sub

Private Sub Install_Click()
Dim objRootKey As RegKey
Dim objStartKey As RegKey
Dim objValue As RegValue
Dim iNumber As Integer
Dim iRetNumber As Integer
    
Const stSubRoot1 As String = "Software\Microsoft\Office\10.0\Excel\Options"
Const stAddin As String = "C:\DDE\Test.xla"

'The predefined root-key.
Set objRootKey = RegKeyFromHKey(HKEY_CURRENT_USER)

'Parse the subkey.
Set objStartKey = objRootKey.ParseKeyName(stSubRoot1)

iNumber = 0

'Retrieve the highest OPEN-number.
For Each objValue In objStartKey.Values
    If objValue.Name Like "OPEN*" Then
        iRetNumber = CInt(Val(StrReverse(objValue.Name)))
        If iRetNumber > iNumber Then iNumber = iRetNumber
    End If
Next objValue

'Add the value to the subkey.
objStartKey.Values.Add "OPEN" & iNumber + 1, """" & stAddin & """", RegValueType.rvString

'Release objects from memory.
Set objValue = Nothing
Set objStartKey = Nothing
Set objRootKey = Nothing

End Sub