Hey marioman99878. About the HDD swapping - I don't see a logical reason, why this shouldn't work. It's like upgrading the HDD. You'll have to have both drives setup for the PS4 as shown in this article here: http://www.radioplaystation.com/blog/ps4-how-to-swap-your-hard-drive/ (go to Post Hard Drive Installation and follow the instructions). Basically this should allow the PS4 to work with both drives. But if anyone has tried this it would be nice if you can get a definite answer.
Also, you could upgrade to a larger capacity drive as @game junky suggested. And actually you're not limited to the 2.5" form factor anymore, take a look at the first answer in this thread and the link in it...