I believe the best way to do that would be the FO4 configurator in utilities on the Nexus. You would use that to clean up the ini possibly, which is a command at the end, and you would only need that if this was a very old install of the game. From there the configurator will launch the default game launcher which will allow you to pick your shadow settings then resetting them to the Bethesda defaults, finish that, then tweek the shadow settings with the configurator. You would do this in stages an test it as you go. *burp* most of the time I don't actually end up touching the .ini anymore, just whatever the configurator will set in the .ini for me. In particular Shadow DIR an LOD was helpful in the later update for that app. You would just do all that work in testing an playing with it to produce your perfect set up, which sucks, but the pay off is nice.