The Name Manager in both Excel for desktop and Excel for the web enforces a character limit on the Comment of Name Manager names. You cannot even type or paste more than the allowed number of characters.
However, in the Advanced Formula Environment, not only can you enter more than the allowed number of characters in the Description (which corresponds to the Comment in the Name Manager), but you can save this change to the name. If you enter too many characters, the workbook will become corrupted. This happened to me in Excel for the web.