Just like flash files, there are decompilers available that can edit dll files. A search reveals that .NET Reflector with a plugin called "FileGenerator" will do the trick.
You can't open or modify DLL files.
This is a first person mod for Skyrim: http://www.nexusmods...im/mods/57859/? - it consists only of two Script Extender files: one .ini and one .dll... But how to open this .dll file and modify it, is beyond me...
Yes, I tried with the .NET Reflector, but failed to open the file. I didn't know about the plugin though, so I think I will give it another try. Thanks!