CREATE TABLE MyTable
    (MyPK           INT PRIMARY KEY
    ,othercolumn    VARCHAR(10)
    ,deleterecord   CHAR(1) DEFAULT('0') CHECK (deleterecord IN ('0', '1'))
    ,deletereason   VARCHAR(200) DEFAULT(NULL))
GO
CREATE TRIGGER MyTable_delete ON MyTable
INSTEAD OF UPDATE, DELETE
AS BEGIN
    UPDATE t
    SET deleterecord = i.deleterecord
        ,deletereason = i.deletereason
        ,othercolumn = i.othercolumn
    FROM MyTable t
    INNER JOIN INSERTED i ON t.MyPK = i.MyPK 
    WHERE (i.deleterecord = '1' AND i.deletereason IS NOT NULL) or i.deleterecord = '0'
END
GO

INSERT INTO MyTable (MyPK)
SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3

SELECT *  FROM MyTable

DELETE FROM MyTable WHERE MyPK = 1

UPDATE MyTable SET othercolumn = 'EXAMPLE' WHERE MyPK = 1
UPDATE MyTable SET deleterecord = '1' WHERE MyPK = 2
UPDATE MyTable SET deleterecord = '1', deletereason = 'MY CHOICE' WHERE MyPK = 3

SELECT *  FROM MyTable

DROP TRIGGER MyTable_delete
DROP TABLE MyTable