Hi,
TW has 2 types of tiddlers. There are "standard" content tiddlers, which are created by users. User created content always wins!
Then there are so called "shadow" tiddlers. Plugins and the "core" tiddlers are shadow tiddlers. That means, if you change them "after a warning" they become content tiddlers. So your changes always win..
BUT if you messed something up, you can delete the content tiddler and the "shadow" tiddler will take over again. So you are pretty safe.
The ControlPanel : Info tab, has a info named "Overwritten Shadow tiddlers". ... If you click the "search" icon, you'll get a list of all shadows, you have changed. So it's easy to find out, what you changed.
-mario