Update MySQL slave when changing the hostname/IP of master
Once you change the MASTER_HOST, everything else needs to change with it.

The "dark back-alley" approach you just suggested is exactly what to do.
    

Warning: Some systems use "mysqld" versus "mysql". 
The --skip-slave-restart "option" may not available without editing your
/etc/init.d/mysqld script to include this as a new option. 
If used, it will still start the slave upon startup.&lt;/p&gt;


On the Slave, run these four lines:

cd /var/lib/mysql  
service mysql stop  
cp master.info master.info.bak
wc -l &lt; master.info


The last line echoes the number of lines in master.info

Next, vi master.info and change the IP address.

Next, run wc -l &lt; master.info and make sure the linecount is still the same

Next, start mysql without starting replication

service mysql start --skip-slave-start


Login to MySQL, and run

SHOW SLAVE STATUS\G


If the IP address you added appears, then run

START SLAVE; SELECT SLEEP(5);
SHOW SLAVE STATUS\G


If you see Slave_IO_Running : Yes and Slave_SQL_Running : Yes, Congratulations !!!

Give it a Try !!!