I don't understand the question.
Any version of Lightroom displays previews in the Library module, they are created automatically for you, and you can't turn this off. You can adjust the size of the previews and how long they are kept before being deleted.
So could you explain further what you mean by "Can I create previews from existing LRCC images?"
I am sorry dj_paige, I left out an important word. "SMART" previews. If I understand them correctly, they will remain on the CPU without needing the original file thats stored on external hard drive. The benefit being, smart previews take up less space.?.
Smart previews remain on the same disk (not CPU) as your catalog file even when you disconnect the drive.
You create them via Library > Previews > Build Smart Previews
The benefit is that if the external disk or network drive is disconnected, you can still edit your photos. If space is a problem, this usually refers to photos on an SSD, and then yes you can save some space by creating smart previews and then moving the photos, but I don't see why you'd want photos on an SSD anyway.
I am storing all raw images on external and needed to know how to build smart previews after the fact, since I was not "smart" enough to do it when I loaded them from CF. I wanted the smart previews on my MacBook without staying tethered to external hard drive.
I guess I explained what I was wanting better as time went on. Your answer was what I needed. Thanks a million, and 1.