Change sparse attribute from an .iso file on Windows 8.1

You can control whether the file is set as sparse or not by running (from an elevated command prompt) fsutil sparse setflag <filename> 0|1

To turn off the sparse setting, run:

fsutil sparse setflag YOURFILENAMEHERE 0

To turn it back on, run:

fsutil sparse setflag YOURFILENAMEHERE 1

and to query it:

fsutil sparse queryflag YOURFILENAMEHERE

I found this by trial and error and a search on TechNet - I don't go around setting or unsetting sparse files so I can't speak to any risks from doing this, other than the file(s) will take up much more actual space than they might have otherwise.