It's best if you just change everything inside the game (providing you can enter the game). Otherwise, there's always Notepad and Wordpad (open up the config file -- it's a regular XML, and is quite easy to understand).
I might make the ultimate config app sometime, but first I'll have to figure out how to embed the Aquaria banner and how to actually edit the XML (AutoIt3: I've tried this one XML wrapper, but it seems a bit complicated. Maybe I should read the documentations).