Excel and DateTimes are always a tricky combination… Excel will often interpret those attributes in a different way.
If I understand correctly, you want to show the ‘+2’ in the Excel when you create the export.
Excel doesn't show this in a field if it interprets the field as containing DateTime-information.
If you only want to show this data in Excel, you're better of exporting the attribute as a String. That way you can use a conversion-microflow which transforms your Mx-DateTime attribute to a string to show the timezone information, and Excel won't interpret the data as a DateTime field (and subsequently change the way the data is shown in Excel).
This is with the assumption that you're talking about the Excel Exporter module and not the default button on a datagrid.
If you're talking about the second, you would have to create a separate attribute to show the data containing the timezone information and export that from a grid.