Moving entire current site under new subdomain

So I have a fully functioning job portal up and running now at domain.com

We want to focus more on our core business, which is head-hunting, and we’d like to go for a landing page focusing primarily on this. What we would like to do, is list the new fancy landing page under domain.com, and then move the entire current website with all the sub-urls under a new subdomain: domain.com/portal/*

Now, is there an easy way to go about this? So far I have found something mentioning that editing the .htaccess file should be sufficient? Any other considerations with regards to the database, etc.?

Thanks