Here's one of my own assassination hypotheticals that I wanted to bring up:
1) You could either prevent the assassination of Grand Duke Sergei Alexandrovich of Russia, or have his assassination carried out a lot earlier by having Ivan Kalyayev not notice the children that accompanied the Grand Duchess Elizabeth inside the carriage, also leading to their deaths as well. Would a bloodier assassination of both Grand Duke Sergei Alexandrovich, his wife, and his adopted children Grand Duchess Maria Pavlovna and Grand Duke Dmitry Pavlovich result in a bigger crackdown on revolutionary activity, or would an overreaction result in civil war?
2) Preventing the Lisbon Regicide by stopping the assassination of King Carlos I of Portugal and the heir apparent at that time, Dom Luis Felipe. I wonder if this would result in a continued survival of the Portuguese monarchy if Carlos I of Portugal had survived, or if the assassination attempt failed, would it result in a civil war breaking out between monarchists and Portuguese republicans?