Hmmm... the abiliy for NTSC4NTSC to display everything on an NTSC-only monitor sounds like a nice feature.
The same can probably (?) be done with Degrader by playing with the 50Hz and 50HzSystem options. I've always had my Amigas running through a NTSC/PAL monitor, so I've never had to force compatibility on that levelk. You don't need to reboot to make Degrader take effect, though - the SurviveNoReset option will kick in your settings instantly.