it is imperative that you hang on to the old passport and keep it safe. When you transfer the visa from one book to another, the new passport will only have a stamp, not a visa. Somewhere along the way after, the IO will ask for a copy of that visa from the old passport. UD IO pulled that trick this year on me when I renewed my visa extension this year.
If you lose the original visa depending on your renewal schedule, you may be taking a trip to Laos and their Embassy there to get a NEW VISA.