Is it possible to edit plist files using their xml format ?

I explain:

in /Library/Preferences, I have a lot of .plist files (e.g. /Library/Preferences/com.apple.SoftwareUpdate.plist).

When browsing this folder in the Finder, I can preview (using QuickLook) those files in their xml format.

But if I try to open this file

- with TextEdit, I get some binary version like this:

bplist00fl

## % &( #_ LastSuccessfulDate_ IgnoringUnseenRamped_ LastAttemptSystemVersion_ LastBackgroundCCDSuccessfulDate\SkipLocalCDN_ DidRegisterLocalUpdates_ lastDownloadError_ LastUpdatesAvailable_ LastRecommendedUpdatesAvailable_ AutomaticDownload_ RecommendedUpdates_ LastFullSuccessfulDate_ PrimaryLanguages]

... and so on ...

- with nano editor in Terminal (nano /Library/Preferences/com.apple.SoftwareUpdate.plist), I get the same.

- with pico editor in Terminal (pico /Library/Preferences/com.apple.SoftwareUpdate.plist), same again.

Moreover, when I edit the file using pico or nano, Finder & QuickLook can't provide a preview anymore, and the file modified this way is overwritten at next use

(in this case, at the next Software Update check) by its old version.

Here is my question:

is there a way to edit the xml version of the plist, and save it in a way OS X will take your changes into account ?

And yes, I know there are lots of third-party apps which can do this, but I would rather prefer to get a way to do this without any extra install or utility, only using the OS X built-in tools.

Is this possible ?

Thanks to those who will read me, big thanks to those who will take some time to answer 😉