I'm trying to achieve the following mapping
keycode 135 = <Ctrl-C>
Is it possible to achieve this in some way?
That's not possible with xmodmap. I don't think it's possible with XKB either, but I'm not sure.
Is your aim to have a key that's always identical to pressing Ctrl+C (e.g. in a terminal, it would interrupt the running program), or to have a clipboard copy key? If the latter, try
If you're on Ubuntu, and possibly even if you aren't, the recommended method to set up additional (“multimedia”) keys is keytouch.
If you really want the key to be equivalent to Ctrl+C, your desktop environment or window manager may let you bind the keysym to a command that generates key press and release events for that key combination. If you prefer or must use a DE/WM-agnostic method, you can use xbindkeys to bind an arbitrary shell command to a key, and xmacro to manufacture key events to send to a window. You'll still need to have a keysym associated with the key; a good choice is
You'll need to start