For step 3 I'd rename the directory to make the magic happen, with that method there is no confusion down the road. Your method of repointing via the panel also works, but 5 years later someone could end up pulling there hair going "wtf why did they do that"..or worse, "I can't figure out why it works this way." To rename the directories what you would actually want to do is make the .org a "fully hosted" domain using the same USER as the .com. When you do that the dreamhost panel will add a directory for the .org... once it has been created you would:
mv example.com TEMP
mv example.org example.com
mv TEMP example.org
With Wordpress there will also be additional database updates needed. Wordpress stores full absolute links (i.e including the domain name) in the database. Two methods are use phpmyadmin to manually update, or there is also a Wordpress plugin that can be used.