Applies a sensitivity label to a Word or Excel file using openxlsx2 and built-in XML. Supported labels are 'Personal', 'OFFICIAL', and 'OFFICIAL_SENSITIVE_VMO' (visual markings only).
The function loads the file, applies the specified sensitivity label using the appropriate XML, and saves the modified file. If successful, it silently returns the file path.
See also
Other Sensitivity Label functions:
read_sensitivity_label()