I use Notepad++. I simply load the .lsdl file, edit it, and save the edited .lsdl. No problems so far. As you can see, it's simply a straightforward process without any need for file conversions.
I used it for one of my leagues where I edited a league with an 82-game schedule. I changed the schedule so that teams played only 3X a week.
If you're interested you can download it for free at: