In QL? = not possible. Many people tried and the best you can do is to make a super bright cfg and use dark enemy model + dark crosshair i guess, search the forum there is 2 or 3 diff cfg like that.

use Wide beam, it's slightly transparent but makes a huge differance.

You mean for playing with? Certainly not. In my opinion this would be considered an exploit/cheat.

It could be possible in wolfcam like if you're trying to make some kind of unusual frag movie, but I wouldn't know how to do it.

It was possible. I forget which cvar, but it was definitely possible - I used it, though it felt pretty odd. Probably shouldn't have told people about it because it was shortly after I did that it got blocked, haha.

Don't see how it would be considered an exploit/cheat, would consider it more of an achievement if anything, playing without an LG beam would be kind of weird :(

in cpma

You used to be able to do it, I did, but they fixed the cvar so that you can't any more.