Can Legal Name be used as a token?
In order to use legal_name against your message template the best way would be enabling CIVICRM_MAIL_SMARTY to 1 in civicrm_setting.php
By doing this you can access {contact.legal_name} in your message template
I did made a test against Version 4.7.15 which worked. so please give a try
Reference: https://wiki.civicrm.org/confluence/display/CRMDOC/Smarty+in+mail+templates
I guess this helps!!!