The workbook (the *.twb file) is just an XML document, which is just structured text, so if you (carefully) edit the *.twb file with a text editor you can do that.
Make sure you save a copy first - it's very easy to get it wrong and make the workbook unusable.
Thank you very much. Your response was very helpful. I have related question. However, I will start a new new thread for it.