Providing it is just nailed to the wall and not glued, removal shouldn't be too difficult. Take a punch and drive the nails through the boards (assuming it is put up with finish nails). Putting it back up vertically would work if you don't mind working in some short pieces. You will see the splices, but if you spread them out, hide them behind furniture, drapes, etc, it may look OK. You may need to plan for running out though. Every time you cut square ends you will lose a few inches of length. Depending on the layout and how much is reuseable, you may not be able to cover everything again. Can you get more of this paneling to match? If not you may need to get creative with how you put it back up. You could put it on as wainscoting on one wall, then drywall & paint the rest of the wall, just to break it up a little.

Adding windows/doors (especially with creative use of draperies), cabinets, fireplace couldÂ

Wide baseboards and trim along the ceiling may help as well.

Thanks, I didn't expect to be able to cover everything. I actually am thinking of adding a large patio door...
Thanks for the tip on HOW to remove it! Didn't think of that.