Yes it is possible in 2 ways:
+ quickly on the fly. Once your table is created you're allowed to navigate it and highlight the categories you would like to group, by simply clicking on them. Once highlighted (in yellow), right-mouse click and a new pop-up window will allow you to give the group a name and decide if maintain also the 'base' categories or replace them with the group. You're also entitled to choose whether to place the group at the top or at the bottom of the categories list.
+ creating a new calculated variable, by assigning the categories (in the formula field) you would like to combine a unique code value that at your choice can be higher or lower, depending where you would like to see it in the table. In this way the group is like a new category. The categories that will not enter the group can maintain the same coding.