I don't think that scintilla (the component used for editing on codeblocks) supports that, but you could check on http://scintilla.sourceforge.net/
It actually does, but you need to implement it.
You can use one of Scintilla's 5 margins and:
- add new margin to the left -> define it as symbol margin
- register two images -> red marker and green marker
- in the EVT_SCI_UPDATEUI handler (i think maybe EVT_SCI_MODIFIED is enough but need to check it) -> if the line was modified, add red marker to that line
- when saving the file, you can simply replace all markers on that margin to green or remove them
Not too complex,
Eran