Stat > DOE > Modify Design > Taguchi
After creating a Taguchi design and storing it in the worksheet, you can use Modify Design to make the following modifications:
By default, Minitab will replace the current design with the modified design. To store the modified design in a new worksheet, check Put modified design in a new worksheet in the Modify Design dialog box.
Modification
Modify factors in inner array: Choose to rename factors or to change factor levels, and then click <Specify>.
Modify signal factor: Choose to rename the signal factor or to add new levels to the signal factor, and then click <Specify>.
Put modified design in new worksheet: Check to have Minitab place the modified design in a new worksheet rather than overwriting the current worksheet.