Can't think of any way of doing this that doesn't involve replacing the formulae for days past with a static value.

You could do this using the Workbook_Open() event, Worksheet_Change() event and others, but the workbook would then have to be a macro-enabled one. For example: 
Private Sub Workbook_Open()
    Dim resp As Variant
    resp = MsgBox("Would you like to prevent past data from being changed?", vbYesNo, "Question")
    If resp = vbYes Then
        With Arkusz1
        
            ' first sort so we know things are in chronological order
            ActiveWorkbook.Worksheets("Sheet1").Sort.SortFields.Add2 Key:=Range("C3:C45"), SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal
            With ActiveWorkbook.Worksheets("Sheet1").Sort
                .SetRange Range("B2:E45")
                .Header = xlYes
                .MatchCase = False
                .Orientation = xlTopToBottom
                .SortMethod = xlPinYin
                .Apply
            End With
            
            ' loop through the dates until we get to today's date:
            For Each d In .Range("C3:C45")
                ' replace formula with value if earlier than today
                If d.Value < Date Then
                    d.Offset(0, 2).Value = d.Offset(0, 2).Value
                Else: Exit For
                End If
            Next d
        
        End With
    End If
    
End Sub
Would that do the trick?

Tim