I have an xml file which holds a set of "game" nodes (which contain details about saved gameplay, as you'd save your game on any console game). All of this is contained within a "games" root node. I'm implementing save functionality to this xml file and wish to be able to append or overwrite a "game" node and its child nodes within the "games" root node.
How can this be accomplished with xmllite.dll?
You can't physicaly "rewrite in place" any text file (including an XML file) except in the rare case you can guarantee that you're overwriting exactly as many bytes as were there. What you always need to do is to write a new file (which has parts from the old one and parts that are new), then rename the old file (e.g. add a .bak extension to it, after removing any older .bak that might have been left hanging around), rename the new file to the old name, and only at this point remove the old file. This approach guarantees that a computer or disk crash in the middle of your work won't be a disaster -- either the old or the new data will be around (at worst you'll need a rename if the crash is just between the two renames).
To write a new file, with mods and lots from the old one, in xmlfile, use the reader functionality documented here and the writer functionality documented here. For a small file, you can first build a tree of objects in-memory via the reader, then write it all out via the writer; but that can take a lot of memory. The alternative is an incremental parsing approach such as the one the MSDN docs call a "pull programming model".