If it doesn't require re-start, then there must be some specific Nvidia API to make that happen, because from my testing, just updating the registry with the new custom modes didn't have any effect until next session. A different matter is whether this API is documented. Nvidia's API is NVAPI (
https://developer.nvidia.com/nvapi), but I can't get anything clear out of that (probably need further reading).
Both Nvidia and ATI must have these options in order to make new video modes available without rebooting. ATI does have the "timing overrides" feature from the ADL SDK, it's the 'new' method, different from the one we're using in GM, but unfortunately it is not as reliable as the old one, it will re-cook our values if it feels like doing so, it won't work with low resolutions, etc., It's not an usable method.
It's not that ATI cards are especially good or anything, it's just a strike of luck that the old drivers allowed dynamic modelines under Windows, it's not the case with the newer versions, as this was probably an unintended feature.
Anyway I'll keep an eye on any information that might be used to extend the support to Nvidia cards. By now, the best option for NVidia is GM + Soft-15khz + Powerstrip.