Option Explicit

Private Sub UserForm_Initialize()

    Dim ws As Worksheet
    Dim ctrl As MSForms.Control

    Set ws = ThisWorkbook.Worksheets("Stammdaten")

    For Each ctrl In Me.Controls

        If TypeName(ctrl) = "TextBox" Then

            'Darstellung
            ctrl.Font.Size = 12
            ctrl.Height = 24

            'Wert anhand des Tag-Feldes laden
            If Trim$(ctrl.Tag) <> "" Then
                ctrl.Value = ws.Range(ctrl.Tag).Value
            End If

        End If

    Next ctrl

End Sub

Option Explicit

Private Const APPLY_FORMATTING As Boolean = True   ' Schalter: True/False

Private Sub UserForm_Initialize()

    LadeStammdaten

    If APPLY_FORMATTING Then
        FormatiereTextBoxen
    End If

End Sub

Private Sub LadeStammdaten()

    Dim ws As Worksheet
    Dim ctrl As MSForms.Control

    Set ws = ThisWorkbook.Worksheets("Stammdaten")

    For Each ctrl In Me.Controls
        If TypeName(ctrl) = "TextBox" Then
            If Trim$(ctrl.Tag) <> "" Then
                ctrl.Value = ws.Range(ctrl.Tag).Value
            End If
        End If
    Next ctrl

End Sub

Private Sub FormatiereTextBoxen()

    Dim ctrl As MSForms.Control

    For Each ctrl In Me.Controls
        If TypeName(ctrl) = "TextBox" Then
            ctrl.Font.Size = 12
            ctrl.Height = 24
        End If
    Next ctrl

End Sub