In order to copy an offer to a new period visit Rates > Offers section and find the offer that you need to copy. Move your mouse over the offer and you will notice four icons on the right side of the offer's title.
Click on the second icon (copy icon) and choose whether you need to copy the offer to the current pricelist or to another one.
As soon as you click on Copy the new offer will be created into the pricelist of your choice and will have the same name with the original offer, accompanied with -copied.
Enter in the new offer, update its name, its rules and its policies and make sure that you click on Activate this Offer in order to publish it.