I've got a question. In Method 2, you've got:

CREATE TABLE DESTINATION_TB(

ID INT IDENTITY(125006,1) NOT NULL ,DATE DATETIME ,COST MONEY)

INSERT INTO DESTINATION_TB (ID, DATE, COST) SELECT ID ,DATE, COST FROM SOURCE_TB

DROP TABLE SOURCE_TB

EXEC sp_rename 'DESTINATION_TB' ,'SOURCE_TB'

But won't that fail, because you're trying to insert into an IDENTITY column the value from the old SOURCE_TB?