The above code will be part of the js/main.js file. You will have to modify it. You can specify any default URL of your choice – best to create a separate page which has links to various OS download pages just in case Javascript fails or when you are not able to detect the OS. You can control the default href through the options panel and hence can change anytime.
I will consider adding option for this if there are more requests for the same. Till then, the above script should be a good enough solution. Hope you agree. Thanks.