I believe that TAGSETS.EXCELXP gives you ways to hide or freeze particular columns, but does not provide a method for protecting columns. I think this is because the method of protecting columns happens from an Excel drop down box that may not have an XML or Spreadsheet Markup Language tag that is "not" produce-able by TAGSETS.EXCELXP.
You may want to check with Tech Support whether this might be possible at all with other tagsets, such as TAGSETS.TABLEEDITOR or not.
if it's not there yet, I think it might be introduced to the tagset "real soon now" ;-)
See the developers paper "Paper 031-2010 ODS ExcelXP: Tag Attr Is It! Using and Understanding the TAGATTR= Style Attribute with the ExcelXP Tagset" at