how can I override console.log() and prepend a word at the beginning of the output?

You can override the console.log easily

(function(){
    if(window.console && console.log){
        var old = console.log;
        console.log = function(){
            Array.prototype.unshift.call(arguments, 'Report: ');
            old.apply(this, arguments)
        }
    }  
})();

console.log('test')

Demo: Fiddle