Dear,
You can assign exciting category to new group.
Select the category
Press the select element or F2
Select the Not Assignt (at bottom of the screen)
Press the Element/Group or F5
For creating a new no. range
Select Group at Menu Bar
Select Insert
Now give he Text and give the no. range.
Also in table T370T for required category you can maintain the number range.
Regards,
R.Brahmankar