ColumnOrder [Table.2,Material] 2

ColumnOrder [table,column] n

n is the new column number, i.e. n=1 means that the column should be the first column that is displayed, n=2 the second.
The table name should be specified if there are 2 or more tables on the screen and the column name is not unique. You name the table by its title, if a table title is shown, or otherwise as Table, Table.2, ... If you click on View->Screen elements in GuiXT you see the correct name of the table.

The position of all other columns is unchanged.
If the table is already customized by normal SAP means, and you use GuiXT in addition, then the GuiXT script overrides.