I suggest you to use MYSQL trigger :
DELIMITER $$ CREATE TRIGGER topseller_int BEFORE UPDATE ON eav_attribute FOR EACH ROW BEGIN IF NEW.attribute_code = 'topseller' THEN SET NEW.backend_type = 'int'; END IF; END;$$
DELIMITER ;
DELIMITER $$
CREATE TRIGGER topseller_int BEFORE UPDATE ON eav_attribute
FOR EACH ROW
BEGIN
IF NEW.attribute_code = 'topseller' THEN
SET NEW.backend_type = 'int';
END IF;
END;$$
DELIMITER ;
So that the backend-type of the attribute will always remains as you described. Hope it will help you.
