Although I have not heard of a tool to do what you want, it is potentially possible with a Macro.
You mention standalone and embedded text strings
Can you be more specific. Is standalone just text in a cell and are embedded text strings embedded in charts, text boxes etc.
In Visual Basic in Excel most items are present as 'collections' and it is possible to loop through all members of a collection without knowing how many members there are. For example you can loop through all worksheets in a workbook and loop through all ChartObjects on each worksheet, so accessing particular items repetitively is not too difficult.