Thanks Sebastian again. I read your answer on Stackoverflow and I looked at the example in the new source. It seems to me however that your example would replace all newly created sheets with an instance of my custom Worksheet. The example you gave on Stackoverflow replaces only the ones with a specific name, but this would not work for me either.
In my case I basically would have "regular" Worksheets and my custom worksheets mixed in the same workbook and I want to be able to tell which ones are the custom ones (and use their custom functionality) depending on the sheet.
In my case I basically would have "regular" Worksheets and my custom worksheets mixed in the same workbook and I want to be able to tell which ones are the custom ones (and use their custom functionality) depending on the sheet.