Here's my scenario: I applied for a Schengen visa at the German Embassy in Manila with the following itinerary: Spain 4 days, Germany 6 days, Austria 3 days, Hungary 3 days, then go back to Spain to depart for Manila. My entry and exit points are in Madrid. Eventually I've been granted with a multiple-entry visa good for a month.
However, recently we've wanted to go to Croatia as well (blame it on Game of Thrones) to see Dubrovnik. So we want to change our itinerary only by replacing Hungary with Croatia, while maintaining our visit duration to all other countries (ESP-GER-AUS-CRO). We will still enter and leave for Manila via Madrid. Is this possible? Will this change be taken against me on my future visa applications?
I initially thought that Croatia had made it to the Schengen area this 2017, only to be clarified that they haven't yet (maybe next year). They're part of the EU though but not Eurozone. I searched if they accept Schengen visas at their border. I found that they do as long as the Schengen visa is either double or multiple entry and if there's no problem with the validity (i.e. the visa should be valid throughout the stay in Croatia), which I have no problem with because mine is a multiple entry type C visa. So it seems on the Croatian side I won't have a problem.
How about for Schengen area authorities, since we'll go back to Spain to catch our ultimate flight out of Europe? I know they can be quite forgiving with itinerary changes, but how about for this scenario of mine?