I buy the Interrail Pass for 3 days. When I use a train connection over night, starting in 22.40 until 00.11 and change the train at 0:30 until mid next day, do the second train counts into the first travel day? Its part of the connection for reaching my destination.
And If not, am I able to keep my reservations for seats by changing my pass?
NO, this is not so. A travelday covers all DEPartures on a calenderday=untill 23.59 the latest, you can in any case still finish the trip, on the train you were on till after midnight, or even on a nighttrain till destination. But from 0.00 the new day starts.
Its quite logical: otherwise could do a 4 day trip from PorTugal to FInland on 1 travelday, as its a lot of connections.
If you can tell us for what day or what connection you ask this, perhaps we can give alternative suggestions to save you that travelday. Or by yourself: find train on bahn.de, click on train nr, then you see all stops from start till end. Find a stop <23.59 and check how you can reach that station-then you could do it! You can travel as you like on a travelday-even going same line backward! Note that about any nighttrain needs also a REServation
(note-untill some years ago there was a different rule-that is why some people get confused).
Ok, thank you, I got it!
And concerning my second question: I now want to change the interrail pass for having more traveldays. Can I transmit my bookings and connections into an other pass, by exchange them?
Reservations are usually not realated to a specific pass and can be used even with a new Interrailpass :)
but as i usually didn´t use the reservation tools of Interrail itself (i prefer to reserve directly with the operator or at the train station) and because of that are not 100% sure maybe 
Reservations are indeed not linked to a pass; they're completely separate.
Note that you can only exchange a pass if you have not used any travel days yet.
Hi, just to confirm, reservations are usually not connected to a Pass like Seewulf and Rvdborgt already mentioned, so it is generally possible to exchange a Pass and keep the same reservations. The only exceptions, as far as I recall, are the Italian reservations, as these have the Pass number printed on them. In those cases you can just ask to have your reservation ticket exchanged at the train station.
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