defaults write help (Mac)

Question

I am trying to set a preference for Firefox to open in 32bit mode on 130 macs via Apple Remote Desktop. The easiest way to do this usually is with defaults write unfortunately I havent found any documention on this, and I cant figure out the syntax for writing a string thats not at the root level.

The file is ~/Library/Preferences/com.apple.LaunchServices.plist

I need to change the string x86_64 to i386

<dict>
<key>LSArchitecturesForX86_64v2</key>
<dict>      
    <key>org.mozilla.firefox</key>
    <array>
        <data>
        Ym9va2QCAAAAAAQQMAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
        AAAAAAAAAAAAYAEAAAwAAAABAQAAQXBwbGljYXRpb25zCwAAAAEB
        AABGaXJlZm94LmFwcAAIAAAAAQYAAAQAAAAYAAAACAAAAAQDAABq
        ix4BAAAAAAgAAAAEAwAAWYNjAQAAAAAIAAAAAQYAADwAAABMAAAA
        CAAAAAAEAABBtfgZbgAAABgAAAABAgAAAgAAAAAAAAAPAAAAAAAA
        AAAAAAAAAAAAAAAAAAEFAAAMAAAAAQEAAE1hY2ludG9zaCBIRAgA
        AAAEAwAAAICcregAAAAIAAAAAAQAAEG0QBQYAAAAJAAAAAEBAAA0
        NkFGNUYyOC1DNTExLTM0MEMtQkU1RS1DREYzMTgyQThFOTIYAAAA
        AQIAAIEAAAABAAgA7z8AAAEACAAAAAAAAQAAAAEAAAABAQAALwAA
        AAQAAAADAwAAAAAAIBkAAAABAQAAL0FwcGxpY2F0aW9ucy9GaXJl
        Zm94LmFwcAAAAMwAAAD+////AQAAAAAAAAAQAAAABBAAACwAAAAA
        AAAABRAAAFwAAAAAAAAAEBAAAHwAAAAAAAAAIBAAABgAAAAAAAAA
        MBAAAEwAAAAAAAAAQBAAAGwAAAAAAAAAAiAAACQBAAAAAAAAECAA
        AKQAAAAAAAAAESAAANgAAAAAAAAAEiAAALgAAAAAAAAAEyAAAMgA
        AAAAAAAAICAAAAQBAAAAAAAAMCAAAJwAAAAAAAAAAdAAAJwAAAAA
        AAAAENAAADABAAAAAAAAAP8AADwBAAAAAAAA
        </data>
        <string>x86_64</string>
    </array>
</dict>

Answer 1

I don't think there's a way to do this with defaults (well, there is, but it involves dumping the entire LSArchitecturesForX86_64v2 dictionary, editing it, then reimporting). But PlistBuddy can do the job:

/usr/libexec/PlistBuddy -c "set :LSArchitecturesForX86_64v2:org.mozilla.firefox:1 i386" ~/Library/Preferences/com.apple.LaunchServices.plist

And the usual caveats before deploying anything to 130 computers: test this first (I tried it, once...), and have it back up the relevant file on each computer so if something does go sideways you can roll it back.