How do I make binlog-format=ROW the start up default in the /etc/my.cnf file?
I think your problem may stem from where you wrote the directive

Make sure you place the option under the [mysqld] header in /etc/my.cnf

[mysqld]
binlog_format = ROW


If you place it under any other header, the mysqld process will not see it.

Give it a Try !!!