Buscando encontré esto.
No lo he probado, espero que te sirva.
Cita: Change 'Index Page' title in phpBB3:
1. Edit \language\en\common.php
2. Look for: 'INDEX' => 'Index page',
3. Change 'Index page' to your title.
Change 'Index Page' title in phpBB2:
1. Edit \language\lang_english\lang_main.php
2. Look for: $lang['Index'] = 'Index';
3. Change 'Index page' to your title, for example: $lang['Index'] = 'My Website Adviser Blog';
http://mywebsiteadviser.blogspot.com...ndex-page.html