>What shoud be the datatype of that additional column, if I add it in to the cursor while fetching the data from the back-end. And if I create another cursor with addtional column using TTOD() from the original cursor, at the fron-end, It is read only Cursor.

Use a view or the following undocumented trick:

SELECT field1, field2... ;
FROM SqlDB ;
INTO CURSOR cReadOnly

USE DBF("cReadOnly") AGAIN IN 0 ALIAS cReadWrite