I don't know all the answers for Unreal; here are some sites that will probably contain them. Note that these sites cater to modders and engine developers alike, but some content may not be available without licence. As to exactly what that content is, you'll need to take a look:
http://udn.epicgames.com/Two/WebHome
http://udn.epicgames.com/Two/PublicModResource
As far as I know, all of those things are possible with the engine, but I don't know whether they can be implemented in exactly that fashion in a mod. (The links ought to contain the answer.)
(Edit follows)
See
http://www.chiefdelphi.com/forums/sh...1&postcount=28 for more information: apparently these things are possible in a mod, via UnrealScript. (Except maybe .dll imports, but they would most likely be redundant, due to native formats.)