I don't think you can do this with the native out of the box application. It can be done, but it will take an addin to do it.
The .odt file is a collection of files. (To prove this, take a sample odt file, rename it so it has a .zip extension and WinZip will display these files.) In this "zip" file, you'll find a file named "meta.xml". This is where the document's custom properties are stored.
In short, all the addin needs to do is read/modify the values in the meta.xml file.