1. To start, you need to make sure, which HUD you're using now. To that, in game console type cg_hudfiles command. Console will answer something like that:





2. Go to "Steam\steamapps\common\Quake Live\[your steamID numbers]\baseq3\ui" and open .cfg file frrom prev. step.
3. Usually, this file look's pretty simmilar in all HUD's, except for string that load's in-game HUD. For example:







We need exactly this string. Find .menu file in your "ui" folder and make backup copy of it.
4. Open the .menu file (Notepad++ recommended)

If you're using one of the default HUD's, after step 1 go to "common\Quake Live\baseq3", open the "pak00.pk3" with WinRAR and go to "ui" folder. Open the .txt file from step 1, check which .menu file he calls, and drag .txt and .menu files into path from step 2.
Now you can use defalut HUD like custom, just type in console "cg_hudfiles "ui/[.txt file]"; loadhud"

Now we need put crosshair code into HUD and not destroy everything. The code:
Put this somewere between... something. Not into text or "itemDef" operator's. Try to find empty space between "menuDef" like in screenshot below and put it here and save the file.

After that in game you can type "cg_hudfiles "ui/[.txt or .cfg]"; loadhud", make your default crosshair invisible (by "cg_crosshairsize 0" for example) and if you see black cross somewere in centre — you're on the right way.

So, our workspace to editing crosshair is here:
Now I will decode:
Let's start from choosing one of the default crosshair.

Go to "Steam\steamapps\common\Quake Live\baseq3", open "pak00.pk3" with WInRAR, inside of it go to "gfx/2d". Here's all QL crosshair's. Choose whatever you want (better way to preview crosshair is drag&drop it to the desktop or open it in some graphics software, because crosshair's are white and on the transparent background) and change path in background string, for example:

Save .menu file, do "loadhud" command in game console and check the result.
Now let's change crosshair size and position.

I made my crosshair for 4:3 mode and 1152x864 resolution, so on your display crosshair can be not centered. Start changing position with changing SIZE.

I'm using similar value for width and height, but I'm not sure it's correct for other displays.

So, when you setted up size you want, let's change position.

First of all, enable your default crosshair and set little size of it ("cg_crosshairsize" command) to make sure you will set custom crosshair right to the centre.

I think on your display crosshair won't be too far from the center, so adjust the values by +/- 1-5. All I can say — "+" for the X is "right", "+" for the Y is "down".

List of poses with same width&height, suitable for me:

Save .menu file, do "loadhud" command in game console and check the result.
Now let's change crosshair color.

Go to "style" string.
So, the first first three "0" is R G B encoded from 0 to 1 format (maybe it's CSS RGBA, but idk).

Go to this site[csscolor.ru], choose color you want and take the values from here:
Input values in code, delete commas and this will be look's something like that:

Save .menu file, do "loadhud" command in game console and check the result.
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Nice! If you did everything correctly, now you have custom crosshair which based on your HUD.

Now you can multiple crosshair's like you want. For example, by complaing basic crosshair and HUD's crosshair. I used it for better visibility:
Or you can make crazy meaningless sh-t like this:
Also, you can just add code again, name it's like ///CUSTOM CROSSHAIR 2 for future, and make crosshair harder:
(3 HUD's crosshair's here, I think available value is close to infinite).