To work with Autodesk Vault using VBA (Visual Basic for Applications), you'll typically need to interact with Vault's API. This involves:


1. **Logging into the Vault**: You need to authenticate your application with the Vault server.
2. **Retrieving a file**: Check out or download the file you wish to modify.
3. **Modifying the file**: Perform the necessary modifications to the file.
4. **Saving the file back to the Vault**: Check in the modified file.

Below is a sample VBA code that demonstrates this process. The example assumes you have access to Autodesk Vault's API and that you have the necessary references set up in your VBA environment.

### Sample VBA Code

```vba
Option Explicit

' Include references to Autodesk.Connectivity.WebServices and Autodesk.Connectivity.Explorer.Extensibility

Sub ModifyVaultFile()
    Dim vault As New VDF.Vault.Currency.Connections.Connection
    Dim serviceManager As New Autodesk.Connectivity.WebServices.DocumentService
    Dim fileId As Long
    Dim filePath As String
    Dim localFilePath As String
    Dim modifiedFilePath As String
    Dim checkedInFile As VDF.Vault.Currency.Entities.FileIteration

    ' Connect to the Vault
    vault = ConnectToVault("https://vaultserver", "Vault", "username", "password")

    ' Specify the file ID and local file path
    fileId = 12345 ' Replace with actual file ID
    filePath = vault.FileManager.GetFullFileName(fileId)
    
    ' Download the file
    localFilePath = "C:Temp" & Dir(filePath)
    vault.FileManager.DownloadFile(fileId, localFilePath)

    ' Modify the file (Example: Append text to a text file)
    Open localFilePath For Append As #1
    Print #1, "This is a modification to the file."
    Close #1

    ' Check-in the modified file
    modifiedFilePath = localFilePath ' In this example, we modify the file in place
    checkedInFile = vault.FileManager.CheckInFile(fileId, modifiedFilePath, "Modified the file with VBA")

    ' Clean up
    Set vault = Nothing
    Set serviceManager = Nothing
End Sub

Function ConnectToVault(serverUrl As String, vaultName As String, username As String, password As String) As VDF.Vault.Currency.Connections.Connection
    Dim settings As New VDF.Vault.Currency.Connections.ConnectionSettings
    settings.ServerName = serverUrl
    settings.VaultName = vaultName
    settings.UserName = username
    settings.Password = password

    Dim connection As New VDF.Vault.Currency.Connections.Connection(settings)

    ConnectToVault = connection
End Function
```

### Steps:
1. **Connect to the Vault**: The `ConnectToVault` function authenticates the user and connects to the Vault.
2. **Download the File**: The file is downloaded to a local directory.
3. **Modify the File**: The file is opened, modified (in this case, appending text), and saved.
4. **Check-In the File**: The modified file is checked back into the Vault.

### Prerequisites:
- Ensure that Autodesk Vault Client and SDK are installed.
- Add references to the necessary Autodesk Vault libraries in your VBA environment.

This is a basic template to get you started. Depending on the complexity of the file modification and Vault operations, you may need to add more sophisticated error handling and additional features like file versioning.