At present the direct or download URL to a file on SkyDrive changes regularly. This is arguably a bug. It is widely considered best practice for any URL provided to the public to be maintained.
Apparently, SkyDrive is not meant to be used in this way. However, a wise strategy for SkyDrive would be not simply to deliver exactly what people at Microsoft think SkyDrive should be, but rather to endeavour to deliver what users want and need.
Stop changing direct or download URLs to files on SkyDrive.