This should create a new column with a different name. Modify this example as necessary for your purpose.
Names Default to Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
expr = :weight << Get Script;
Eval(
Parse(
Substitute(
"dt << " || Char( Name Expr( expr ) ),
"weight",
"weight 2"
)
)
);