>Programmatically? AFAIK, no.
>
>>Is there any other way to change the structure of the existing table?

Yes -- there is another way. I used it years ago:

use the COPY STRUCTURE EXTENDED command to create a table of the fields. Then add/delete fields as appropriate. Then use CREATE FROM command to create a new table from the COPY STRUCTURE EXTENDED table. Now you have to populate the new table from the original table. This is not as elegant as the ALTER TABLE command, but it was an "old" way to modify the structure of tables.

The COPY STRUCTURE EXTENDED command could also be used to test for the existence of a field as well...