[Ox1gEN]

You could create the same command, do this:
And return something else. (e.g - use return)

pawn Код:

CMD:mycommand(playerid, params[])
{
    return SendClientMessage(playerid, 0xFF0000FF, "This command has been disabled.");
}

This should and will (most likely - haven't tested it) work.
Don't forget to create a filterscript for it and include it in server.cfg.