I tried to modify my stay with my host Brian and he has told me I need to cancel my entire stay. I send the modified dates and he insist I cancel my reservation.
Attempting to try to cancel my reservation, I would lose my entire amount instead of modifying my stay for a shorter time due to my work schedule.
Shortening a stay will probably lead to some refund for you. Some hosts do not like this. But they can not oblige you to cancel. So you could ask Airbnb for advise, depending on the situation (is it a long term stay ? How many nights shortening on total amount of nights etc..)
@Emiel1@Dalila40 yes, the host can't force you to cancel. But he also is not required to accept a modification request. So if he doesn't want to accept the modification request, then your choices are to keep the entire stay or cancel it.