Currently when I edit the regular expression, the sample text or the replace expression, there's no way how to undo (and then redo) the last modification(s).
I have recently implemented and tested a simple solution which adds the undo/redo support to all the fields (instances of the StyledText class) - please see https://sourceforge.net/p/etinyplugins/blog/2013/02/add-undoredo-support-to-your-swt-styledtext-s/. All that is needed is to take the blogged class UndoRedoImpl (I would leave the package and so on up to you) and use it in the constructor of the project's SWTAdapter class: "new UndoRedoImpl(editor);".
And I'm not against doing a new version of the plug-in myself if you tell me how to proceed correctly...
Modified plug-in jar - with the undo/redo functionality added
CVS 'unified' diff (for Eclipse) which implements the undo/redo feature