Download Manager with replaceable URLs

So the dealio is that I used Getright on my PC for ages. Now I have a Mac so I'd love a download manager for one functionality.

I'd like one that lets me replace the URL of the download to resume downloading a file when it craps out.

I often download from my ISP's mirror server as it's free towards my download quota (yeh, laugh at us Aussies.) However, sometimes the download craps out and I can't resume, since the server only keeps the links active for 5 minutes. So what I'd do is just try downloading the file again, but copy the new link into Getright and it'd resume the file using the new URL.

I'd like an app that does this for Mac, but I can't find anything so far.

Thanks.