Tsuyoshi-san, I hope this information will help you.
The meniscus-lensed VPKs (or any camera, not just the 127 VPKs) are the only ones that can behave in the "soft focus" manner. The periscope and anastigmat lenses will no longer focus properly if you remove their front lenses. The meniscus versions are clearly evident by the lack of any glass in front of the diapragm.
You must remove both the hood and the rotary diaphragm in order to "open up" the lens for the soft focus effect. The resulting f-ratio is now fixed at approximately f/5.6 or so. Since the shutter speed only about 1/25 of a second, you might need a ND filter to keep from overexposing your shots on faster modern films.
Before you start any modifications, check your bellows for light leaks, as the outer material often has become hard and flakes away from the folds, causing numerous pinholes that may fog your film.
Considering those difficulties, you might instead try using a 120-sized meniscus model (like a cheap No. 2 Folding Pocket Kodak)--the effects will be similar, but the 120 film is much more common, and cheaper. These are easier to try because you just unscrew the front hood which was limiting the aperture to about f/11, and then the adjustable iris can open up to its maximum opening, usually about f/7 on these cameras, allowing the aberrations which soften the image.
You might also look into adapting a small magnifying glass lens onto a current SLR or DSLR, as this will give you better focusing ability for close-ups, as well as aperture-priority control of exposure.
--Don