Hi @Daniel38 🙂
Yes, if you go to the guest's reservation and scroll down you can see what cancellation policy the guest booked under. If you choose another policy afterwards it won't change already agreed to reservations. If a guest needs to cancel the guest always has to cancel on her own and she will get refunded automatically by airbnb according to the cancellation policy. As a host you dont have to do a thing. The guest needs to cancel - if you ever receive "a request to cancel" don't ever accept it as it then will look like you cancelled. The guest has to do it from their side alone and you will get an email with the cancellation :-).
Best, Sandra