about repair calibration modding
There are many reasons one might want to modd a CRT monitor: adding extra signalinput or modifying the behavior of the monitor. There are some use case for art purpose and others more in the retro gaming universe.
For retro gaming, there is a huge interest in getting the best signal into the monitor which usually means getting RGB or components signal straight to the monitor. The retrorgb explains all in details why RGB gives the best picture for retro gaming and a review of consoles and their RGB support.
One way to add RGB to a monitor that does not have it is to do the RGB OSD hack. This will only work on more recent monitors that have OSD support. The details on the RGB OSD hack can be found on this thread on shmups. The modd on many JVC monitors is covered on immerhax website.
Even if the monitor does not have OSD may be possible to modify the input and add composite (if only RF is available) or luma chroma. What can be done depends on the onboard chips present. Then looking at the datasheet will tell the pine-out and supported signal. Usually it is needed to add a capacitor and a resistor. Some trials and error might be needed to get it right.
In some cases you might want to rotate the image of 180 degrees, for instance when using the monitor into an arcade cabinet. This can be achieved quite easily by yoke wires swapping approach. Just swap the two vertical circuit wires and the two horizontal circuit wires.
Some interesting ressources about hacking CRTs to make art: