Rather than editing in the source document, instead you should edit the newly-created symbol file, i.e. drag your selection into the Library List under My Libraries, name it, and then doubleclick on that symbol to open it for editing. This allows you to, for instance, add attributes to the document (i.e. the symbol file) and then link new text fields to those attributes.Whenever possible, you should make edits in the symbol file itself, rather than to a symbol after it has been inserted into a document.
I hope this is helpful.