If the underlying relationship Is good, it seems fairly easy to recover from the penalty. I went from -44 from dowing Brazil twice including one surprise war in the industrial/atomic era to no penalty within 50 turns . Brazil still hated me I'd course and China who is right next to me had other issues. But my diplomacy with the other Civs improved Gandhi went from debouncing to freindly ; Kongo went from denouncing to neutral. Greece went from denouncing to unfriendly (we never had good relations) I can't comment on the penalties themselves but I had expected my diplo game was ruined when I got the penalty. That was not the case.