To recode entries in a column and save the result to the same column, one can select In Place from the drop down menu:

In the JSL code the target column will match the input column.
Hm, Why does the code not work?
a) Short Date() converts the date to a String - but the column is numeric.
b) even after removing short date() it doesn't work. Because Map value() doesn't allow expressions? maybe:

So let's try:
Transfers = New Table( "transfers",
Add Rows( 1 ),
Compress File When Saved( 1 ),
New Column( "OrderDate",
Format( "y/m/d"),
Set Values( [-126144000] )
)
);
Transfers << Begin Data Update;
Eval (Eval Expr(Transfers << Recode Column(
Transfers:OrderDate,
{Map Value( _rcOrig, {-126144000, Expr(today())}, Unmatched( _rcNow ) )},
Update Properties( 1 ),
Target Column( :OrderDate )
)));
Transfers << End Data Update;