When you book, the "fare conditions" determine whether and how you can make changes. We don't expose these in our API at the moment.
When you book a flight, the "fare conditions" determine whether you can make changes or cancel the booking, and if you can, what fees apply.
We don't expose these fare conditions in our API at the moment, either before or after you create an order - we're planning to add this information later in 2020.
In our API, the fare_brand_name attribute on the slices of an offer may give you some clues about the fare conditions - for example, a Basic Economy offer probably won't be changeable or cancellable, whereas Economy Flex probably will be.
To check whether a booking can be changed or cancelled, just get in touch with our support team.