ColumnOrder [Table.2,Material] 2

ColumnOrder [table,column] n

n is the 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 R/3 means, and you use GuiXT in addition, then the GuiXT script overrides.