I want to be able to change the properties of a form, such as borderstyle
and controlbox, during runtime. If it's possible I even want to change the
properties of the form while it is already loaded (visible or not). Is this
possible? If Yes, how?

ControlBox Property

Returns or sets a value indicating whether a Control-menu box is
displayed on a form at run time. Read-only at run time.

Regards.

Add a multi line textbox, a normal textbox, and two command buttons

Option Explicit

Private Const GWL_STYLE = (-16)

' Window styles
Private Const WS_OVERLAPPED = &H0&
Private Const WS_POPUP = &H80000000
Private Const WS_CHILD = &H40000000
Private Const WS_MINIMIZE = &H20000000
Private Const WS_VISIBLE = &H10000000
Private Const WS_DISABLED = &H8000000
Private Const WS_CLIPSIBLINGS = &H4000000
Private Const WS_CLIPCHILDREN = &H2000000
Private Const WS_MAXIMIZE = &H1000000
Private Const WS_CAPTION = &HC00000                  '  WS_BORDER Or
WS_DLGFRAME
Private Const WS_BORDER = &H800000
Private Const WS_DLGFRAME = &H400000
Private Const WS_VSCROLL = &H200000
Private Const WS_HSCROLL = &H100000
Private Const WS_SYSMENU = &H80000
Private Const WS_THICKFRAME = &H40000
Private Const WS_GROUP = &H20000
Private Const WS_TABSTOP = &H10000
Private Const WS_MINIMIZEBOX = &H20000
Private Const WS_MAXIMIZEBOX = &H10000
Private Const WS_TILED = WS_OVERLAPPED
Private Const WS_ICONIC = WS_MINIMIZE
Private Const WS_SIZEBOX = WS_THICKFRAME
Private Const WS_OVERLAPPEDWINDOW = (WS_OVERLAPPED Or WS_CAPTION Or
WS_SYSMENU Or WS_THICKFRAME Or WS_MINIMIZEBOX Or WS_MAXIMIZEBOX)
Private Const WS_TILEDWINDOW = WS_OVERLAPPEDWINDOW
Private Const WS_POPUPWINDOW = (WS_POPUP Or WS_BORDER Or WS_SYSMENU)
Private Const WS_CHILDWINDOW = (WS_CHILD)

Private Const ES_AUTOHSCROLL = &H80&
Private Const ES_AUTOVSCROLL = &H40&
Private Const ES_CENTER = &H1&
Private Const ES_CONTINUOUS = (&H80000000)
Private Const ES_DISABLENOSCROLL = &H2000
Private Const ES_DISPLAY_REQUIRED = (&H2)
Private Const ES_EX_NOCALLOLEINIT = &H1000000
Private Const ES_LEFT = &H0&
Private Const ES_LOWERCASE = &H10&
Private Const ES_MULTILINE = &H4&
Private Const ES_NOHIDESEL = &H100&
Private Const ES_NOIME = &H80000
Private Const ES_NOOLEDRAGDROP = &H8
Private Const ES_NUMBER = &H2000&
Private Const ES_OEMCONVERT = &H400&
Private Const ES_PASSWORD = &H20&
Private Const ES_READONLY = &H800&
Private Const ES_RIGHT = &H2&
Private Const ES_SAVESEL = &H8000
Private Const ES_SELECTIONBAR = &H1000000
Private Const ES_SELFIME = &H40000
Private Const ES_SUNKEN = &H4000
Private Const ES_SYSTEM_REQUIRED = (&H1)
Private Const ES_UPPERCASE = &H8&
Private Const ES_USER_PRESENT = (&H4)
Private Const ES_VERTICAL = &H400000
Private Const ES_WANTRETURN = &H1000&
Private Const ESB_DISABLE_BOTH = &H3
Private Const ESB_DISABLE_DOWN = &H2
Private Const ESB_DISABLE_LEFT = &H1
Private Const ESB_DISABLE_LTUP = ESB_DISABLE_LEFT
Private Const ESB_DISABLE_RIGHT = &H2
Private Const ESB_DISABLE_RTDN = ESB_DISABLE_RIGHT
Private Const ESB_DISABLE_UP = &H1
Private Const ESB_ENABLE_BOTH = &H0

Private Const SB_VERT = 1
Private Const SB_BOTH = 3
Private Const SB_HORZ = 0

Private Declare Function ShowScrollBar Lib "user32" (ByVal hwnd As
Long, ByVal wBar As Long, ByVal bShow As Long) As Long

Private Declare Function SetWindowLong Lib "user32" _
        Alias "SetWindowLongA" _
        (ByVal hwnd As Long, _
         ByVal nIndex As Long, _
         ByVal dwNewLong As Long) As Long

Private Declare Function GetWindowLong Lib "user32" _
        Alias "GetWindowLongA" _
        (ByVal hwnd As Long, _
         ByVal nIndex As Long) As Long

Private Declare Function UpdateWindow Lib "user32" _
                 (ByVal hwnd As Long) As Long

Private Sub Command1_Click()
    Dim L&, S&, O As Object

    Set O = Me

    L = GetWindowLong(O.hwnd, GWL_STYLE)

    'S = WS_MINIMIZEBOX
    'S = WS_MAXIMIZEBOX
    'S = WS_CHILD
    S = WS_SYSMENU
    'S = WS_THICKFRAME
    'S = WS_DLGFRAME
    'S = WS_VSCROLL
    'S = WS_HSCROLL
    'S = WS_CAPTION
    'S = WS_VISIBLE
    'S = WS_BORDER
    'S = WS_DISABLED

    'S = ES_NUMBER      ' this works
    'S = ES_MULTILINE   ' does not work
    'S = ES_UPPERCASE   ' this works
    'S = ES_VERTICAL    ' removes border - unsatisfactory
    'S = ES_SUNKEN      ' does nothing
    'S = ES_RIGHT       ' does nothing
    'S = ES_SELECTIONBAR ' ???
    'S = ES_CENTER      ' does nothing
    'S = ES_PASSWORD    ' does nothing
    'S = ES_READONLY    ' does nothing
    'S = ES_DISPLAY_REQUIRED  ' ???
    'S = ES_NOIME       ' ???
    'S = ES_SYSTEM_REQUIRED ' ???
    'S = ES_NOOLEDRAGDROP ' ???
    'S = WS_BORDER Or ES_VERTICAL  ' no good
    'S = ES_USER_PRESENT
    'S = ES_WANTRETURN

    If (L And S) Then
       L = L And (Not S)
    Else
       L = L Or S
    End If

    Call SetWindowLong(O.hwnd, GWL_STYLE, L&)
    'DoEvents
    UpdateWindow O.hwnd
    O.Refresh
    Me.Visible = False
    'DoEvents
    Me.Visible = True
End Sub

Private Sub Command2_Click()
    Static Flag As Boolean, Q&

    Q = 0
    If Flag Then Q = 1
    Flag = Not Flag

    Call ShowScrollBar(Text1.hwnd, SB_HORZ, Q)
End Sub