Can I download a file in parts? [Chrome]
If you can't do what you want with Chrome's internal down-loader, you can always use an external down-load manager.
I have always found Download Accelerator Plus works very well in Windows, but there are plenty of others to choose from, not only for Windows, but Linux and Mac as well.
You didn't say what OS you're using: this site is a good place to find alternative software for Windows, Linux and Mac, including freeware.