This issue comes up dozens of time on the Japaneseicon forum on gunboards, which includes the authors of the books, Fred Hunnicutt. Doss White, Don, and so many others.

There rifles were not meant to be decocked. You can, and often will, end up with a jammed bolt that will freeze the bolt and render the rifle inoperable. Generally, dry fire is safe. Additionally, many experts claim that springs are not affected by tension and should last the same amount of time under tension as without tension. Many recommend just taking the bolt out, and an open bore and chamber are less likely to rust.

Having read dozens of such treads in the last ten years, attempting to decock a Japanese rifle is like thinking you will win a million on a slot machine in Vegas. You will likely loose and why do it. You may end up spending hours trying to fix bad decision. I would never do it and I have 50 Japanese rifles.