Adding a new column

ALTER TABLE tbl_status ADD COLUMN status_default TEXT;

This will cause an error if the column already exists.  To check if a column already exists first you can use:

PRAGMA table_info(tbl_status);

which will return a table listing the columns of the table.  However many people use the built in PRAGMA user_version) to store an incremental number which you increment as you update the database design (its starts from zero for a new database nless you specify it).