SQL & PL/SQL

I am new to Oracle and using a temp table.

This is my TEMP table.

CREATE GLOBAL TEMPORARY TABLE tt (
c1 int not null
)on commit preserve rows;

After I create temp table, I can find from DBA_TABLES that TEMPORARY flag is set to 'Y'. Where does on commit preserve rows info is stored in the dictionary tables? After I get that info from catalog, can I alter this temp table dynamically to switch from preserve to delete rows.

Your help is appreciated.

Vikram Kumar