you could also insert text fields (with text fields from the form toolbar) for every cell, limit the number of characters for each field then protect your document for forms.
to limit the characters for a cell: right-click on the field, properties, set max length. Then protect the document: tools, protect the doc, choose forms.
this way, users could enter upto the maximum amount of character specified, but not more. This way, your table would not "grow".
regards,