Dune riding is riding a bike on the pipe all day. It will abuse your motor over time. Once in awhile is not bad. My son rode a YZ250F in the dunes years ago at Dumont. It was alright. We did not run paddles. I was on a YZ250 and we just lowered the air pressure. We had no problems running the dunes that way.
Prep wise, like JimYZ said either get another chain or run yours if it allows to move the wheel back far enough. Also do not run tacky chain lube, it will just collect the sand. I cleaned my chain really good before hand and lubed it with WD40 and wiped it down to get off the excess. Sand gets every where.
I hope you are not going to the dunes soon as it is blazing down there. Also I would recomend running some race fuel for higher octane, this will allow the motor to run cooler.
Have fun and post pics of your ride after.