When I assign a key to send a Control-c with the RedirectKey action of xkb, the X server sends correctly a KeyPress with "Control-c" but it also sends a "c" and then the same thing with 2 KeyRelease events.

To do the config quickly, add the following file under xkb/compat/edit

default partial xkb_compatibility "basic" {
interpret.repeat= False;

// Ctrl+C for Copy
interpret XF86Copy {
action = Redirect(Key=<AB03>, modifiers=Control);
};
};

Put "edit" in the compat/complete file:

default xkb_compatibility "complete"  {
    include "basic"
    augment "iso9995"
    augment "mousekeys"
    augment "accessx(full)"
    augment "misc"
    augment "xfree86"
    augment "level5"
    augment "edit"
};

Then you can change the mapping of one of your key using xmodmap:

keycode 69 = XF86Copy

and you'll see the problem with xev.