teylyn and roy; I can see merging cells isn't to smart to work with. However, it works really well for what I am doing. The only thing that stands in my way is the problem of merge / un-merge on a protected sheet. I wonder why this option is disabled. It just doesn't make any sense...

To explain further, the macro I'm using is creates theses blocks by merging cells. However I do not want the possibility to create a block where there are already some content.

Maybe it is possible to only allow this macro to create the boxes in a certain area?

heres the code for creating the merged boxes:
Option Explicit
Dim Col As Integer, Rw As Integer, Ac As Integer, Tx As String

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Count = 1 Then
    If Rw = 0 And Target.Column = 1 Then
        Col = Target.Interior.ColorIndex
        Rw = Target.Value
        Ac = Target.Offset(, 1).Value
        Tx = Target.Offset(, 2).Value
    ElseIf Rw > 0 Then
        If Target.Row >= Rw Then
            Target = Tx
            With Target.Offset(-Rw + 1).Resize(Rw, Ac)
                .Interior.ColorIndex = Col
                .BorderAround ColorIndex:=1, Weight:=xlThick
                .HorizontalAlignment = xlCenter
                .VerticalAlignment = xlCenter
                .WrapText = True
                .MergeCells = True
            End With
            Rw = 0
        End If
    End If
End If

End Sub