Crachou! No OS X 10.11, a preferência é armazenada aqui:
/var/db/com.apple.xpc.launchd/loginitems.{uid}.plist
Para mim, esse arquivo é assim:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>com.github.GitHub.Conduit</key>
<string>com.github.GitHub</string>
<key>version.com.github.GitHub.Conduit</key>
<string>161</string>
</dict>
</plist>