It is possible that your visa application may be denied if you cancel your hotel reservation and book a stay at an Airbnb instead. This is because when you apply for a Schengen visa, you are required to provide proof of accommodation for your entire stay in the country. The Spanish embassy specifically states that they do not accept Airbnb as proof of accommodation, so booking an Airbnb instead of a hotel could be seen as providing false information on your visa application.
It is not uncommon for embassies to request proof of accommodation for the entire stay and for this reason, you should be very careful when making any changes to your itinerary.
If you wish to change your accommodation, it is best to contact the Spanish embassy and ask them if they will accept a different type of accommodation such as a different hotel or hostel. It's also a good idea to have a backup plan in case your visa is denied.
Also, it's worth noting that different countries may have different rules and regulations when it comes to Schengen visa applications. Therefore, you should always check with the embassy or consulate of the country you are applying to for specific information about visa requirements.