On DVD+RW, it simply doesn’t work here: It doesn’t matter if I set the permanent setting and/or the temporary one to DVD-ROM, I even tried DVD-RAM, it doesn’t seem to work. The disc is still identified as booktype DVD+RW in the NEC itself as well as in the PX-716.
For DVD+R, the temporary setting doesn’t seem to work: I set permanent to DVD-ROM and temporary to DVD-RAM (!), the result was a disc with booktype DVD-ROM.
DVD Decrypter confirms that the drive was indeed set to the booktype I wanted it to be set to.