In Unreal Tournament it`s possible to feign death at any position and whenever you want.
You should only feign death, when out of sight of your opponent though, cause it looks too strange, if you just die without a reason, without a deathmessage and without dropping a weapon. There is a workaround for the last thing, just drop your weapon before feigning or use the alias in the control section, but it`s still no good thing to do.
You should also be aware, that you have to stand up again before moving and that takes 700ms, for shooting even about 1300ms.
The only exception to this "feign death - no shooting"-regulation are loadable weapons, the bio rifle for example. If you start loading it before feigning death, you can immediately shoot with it, even before standing up. This is a great comeback tactic, because a fully loaded bio rifle can kill everything in 1 shot and naturally nobody expects that corpses shoot. After shooting though you will need time to stand up and therefore you will be very vulnerable, not being able to shoot or move...
Of course you can also use the RL or even the Impact Hammer like that, but both weapons make too much noise and the RL will shoot after 6 rockets are loaded.
"going for the shield"
"green death by a dead"
Against good players this rarely works though, especially when doing it twice or more.
Besides that there are different methods to find out if you are a real corpse, either by simple shooting, by trying to walk over you (not possible with feign death) or just by keeping the crosshair on the corpse for a second, so that the name appears.
And last but not least, never feign death with the shield. Usual corpses don`t have a big glowing yellow shield around them. But you will have, if you feign death with the shield.