Thank you, dcz, for taking time to reply.
After changing the codes in the phpbb_seo_class.php and after updating the .htaccess, it's working like a charm!
dcz wrote:It's doable, but you'll have to keep the code change in the future updates, not that it will be difficult but rather than it will be a source of confusion if you are not comfortable with coding.
I think I'll be able to handle that. I can code in Java. And probably, I'll start learning php in the next month. So, I don't think it will be cumbersome for me.

dcz wrote:Why would you want to do so ?
Simply because it looks good. I think you should have this as default in the phpBB-SEO mod.
Thanks again.
Soumik