I've been able to have some success in the last few days. It was different to how I intended but it achieved pretty much the result I was after, so I am happy. I have some confusion about how the NVIDIA drivers work though, because it's not very intuitive and doesn't make sense, but it's more of a curiousity since I am achieving what I hoped for (thanks to your CRU tool).
I tried a few different combinations, and what ended up working was switching to PC Resolutions (which for me are paler in colour profile vs HDMI TV Resolutions) and then finding a way to get all resolutions and refresh rates to work that way. In terms of getting Windows to recognise them all. And to avoid the HDMI 'TV' resolutions all together. My goal has been to switch through different refresh rates automatically when a different video file is opened, and then to have consistant colour profiles for each refresh rate. That has now been achieved, although the colour profile looks more like HDMI TV - Limited and is paler and more washed out but I'll get into that later. Because there's a confusion I have about that, in terms of how NVIDIA driver is handling it.
I deleted all of the HDMI TV resolutions @ 1920x1080, but still left the HDMI compatibility, so it does still register within the driver that I'm using HDMI and not DVI. I started using the 'detailed resolutions' like you mentioned to start constructing the refresh rates I wanted. All were too pale/washed out in colour, but I was able to adjust the NVIDIA colour settings in order to compensate, in terms of brightness/contrast/gamma.. so that it pretty much.. 99% looks the same as it did before. It's something like 35% brightness, 45% contrast, 0.88 gamma.
I realised that I could also aim for more than just 23.976, 29.970 and 25fps.. there was enough space in the resolution slots (barely) to include compatibility for other refresh rates, for example 24.000 and 30.000fps videos.. because these videos pop up on YT from time to time. I couldn't include a setting for EVERY video framerate as there's some random ones out there.. but it covers the most common ones. I was lucky to have just enough space in the Detailed resolutions include everything and only had to move the 60hz over to standard resolutions (which worked fine).. and then to use detailed resolutions for the rest. 50hz is my default resolution as this is PAL territory here, so that one is on the top of the list. I guess I'm using the monitor as sort of a computer monitor version of an Australian PAL TV @ 50hz.
So that when I open a 24fps video, it'll use a 48.000hz refresh.. and when I open a 23.976 video it'll use 47.955, for example.. and so far in my testing, everything is staying in sync really well.

Any judders or playback problems are coming from the source video and this is really helpful for me in terms of editting or encoding, in terms of being able to see the difference. My player even has a graph that shows playback in terms of the source video framerate and the monitor/GPU playback.
The NVIDIA driver only recognises 3 of these resolutions as 60 50 and 48. But that's fine because it doesn't need to. Windows recognises them all in terms of changing "screen resolution" in Control Panel and the video player I'm using (MPC-BE) recognises them all as well. So it's a great result and I'm very happy. There are no HMDI TV resolutions for full HD, but that's ok, I don't need them and the colours would look wrong anyway. It's functioning 100% the same as it was before and seems like semantics to worry about it.
The confusion I have is with the colour.. as it's stated that there are
2 colour profiles in terms of the RGB Full vs Limited thing, and the way NVIDIA drivers seem to be handling it seems really dodgy. Because in reality there seems to be 3 (or 4).
1 - The one I was using up until a week ago.. all year.. HDMI TV resolution + Full RGB Colour.. very full and rich colours, probably exactly the same as it would look with a Radeon video card set to full.
2 - PC Resolution - from the 'detailed resolutions' part of CRU. It has a full vs limited setting as well.. this is what I am currently using, with the profile of Full RGB. But it does NOT look like the one I am talking about above. I am running considerable lower brightness and gamma to compensate in order to make it look like "1" above. However after doing this, it does look quite similar, so much so.. that after a few days I can't really tell the difference.
3 - PC Resolution - 'limited' which looks even paler and washed out again. How can this be possible? On paper, an RBG profile is like a curve.. where full RBG is the full colour gamut, and a limited profile is altering the values of 0-16 and 235-255. If it were really applying this in the correct way, how could these 3 settings be possible?
It seems like it's just applying some kind of sloppy and lazy gamma filter or something. And possibly.. it's either applying it twice.. for PC Resolution - Limited, or something similar. Like some sort of inbuilt preset, like it adjusts the preset values of brightness and contrast and gamma or something.
So when you dial up for your monitor and colour settings for HDMI TV Resolution @ Full RGB it's..
HDMI TV - Full RGB - Normal colour
PC - Full RGB - Pale and washed out
PC - Limited RGB- Double Pale and looks awful
But if you dial up your colour and monitor for PC Full, like I currently am now.. it's..
HDMI TV - Full RGB- Very dark and oversaturated
PC - Full RGB- Normal colour
PC - Limited RGB - Pale..
I didn't even mention HDMI TV - Limited, but if I had to guess, I would say that it's something similar (or possibly exactly the same) as PC - Full.
Anyways.. the good thing is, by using your tool I have removed the need to add any custom resolutions via NVIDIA Driver because they seem to always default to PC - Limited - Double Pale.. regardless of setting it to Full or Limited (the change in the menu shows no visible change at all).. therefore for me, with this video card/driver combination.. custom resolutions are useless.
But now.. thanks to discovering this and adjusting my colour settings, I am able to have consistancy of colour through all refresh rates and custom resolutions. And it looks 99% the same as before in terms of colour, saturation, brightness etc. Thanks to your tool..
I am so frustrated with NVIDIA and can't make much sense of any of this above.. it seems really sloppy and amateurish.. not something you'd expect from 2018 technology.. but anyway..
Is there anyway to apply these CRU EDID profile changes permanately to the monitor, or is it always going to be a temporary thing that I need to apply after graphics drivers change, or reinstallation of Windows? Because I already switched my monitor cable back to the original HDMI one, and it reverted all of my settings back to default monitor settings. But luckily I've saved my changes in a bin file and just had to import those back in.. the annoyance is having to readjust colour settings of NVIDIA colour profile but I can always screenshot those for the exact settings and reapply them each time, if needed.
I'd love to find a way to import those bin settings permanately into the monitors EDID, so that it can just run like this forever into the long term. I was able to do something similar to this when flashing my video cards bios, in terms of adjusting the power savings and temperatures at idle but also increasing the speed at peak overclock, it's been 3 or so years and it's been running great in terms of quiet, low power usage but also having power when required. But I understand that the process might be a little bit more complex when it comes to monitors.
Thanks again for your tool, I hope in the near future I can forget about all of this hassle and it can just function like this in the long term.