As usual for editing of hidden preferences for the Finder is done using the defaults command. So, pop open the terminal, and get ready to go. If you want to see the list of currently set settings, check out the command defaults read com.apple.Finder
In addition, when you're done, you'll have to quit and restart the Finder. There are a couple ways to do this. One is to use the command killall Finder. Another way is to use the first mod below to add a quit menu item, which then makes it very easy. Of course, you still have to kill the Finder the first time. Or you could log out and back in, but that takes too long.
We've got a couple commands for you to try. Here they are:
defaults write com.apple.Finder QuitMenuItem 1
This obviously allows you to add a quit command to the Finder. 0 indicates off, 1 is on.
defaults write com.apple.Finder MaximumLabelLines 2
File/Folder names in Mac OS X can wrap to multiple lines! Yay! This command lets you set the number of lines that can be used. 2 is the default, and I'm guessing there's an upper limit, but I don't happen to know what it is, since I like 2. Obviously, change the '2' to whatever number of lines you want.
defaults write com.apple.Finder DebugMode 1
(10.2.x only. sorry )The standard default is 0, with 0 meaning off, and 1 meaning on. Basically, debug mode activates some features of the Finder that are intended... well, for debugging. Among these are the multiple icon sizes menu (submenu of the view menu) and a mysterious Debug menu and a few other examples. Probably most of what you will use this for is the presence of the multiple icon sizes menu. The new size will stick when you turn off debug mode, but if you move the item or change view options, it'll reset. (course, that's true anyway, even in debug mode.).
Of course you can poke around the defaults settings and find lots of other things to change. Most have an easier, GUI way, some are only available through the terminal. A few have a GUI method, but have some values not allowed there.
One last note: as far as reverting goes, the default setting for all the options is listed. If you prefer to do so, you can simply type defaults delete com.apple.Finder OptionName in order to make the setting go away. The Finder will use whatever the default is the next time it is run.