Can I cancel hotel reservation AFTER crossing immigration in Schengen area? [duplicate]

Once the consulate has convinced itself that you can afford to keep yourself housed and fed during your visit, nobody cares much what you actually do. Minor changes in plans, such as exactly where you will sleep, are routine and perfectly allowed.

It would probably be better to have been more honest in the application and say something like "I hope to be able to stay with my friend So-And-So, but in case that doesn't work out, plan B is such-and-such hotel, and you can see I'm budgeting to have that as an option." But really, what they're interested in is just whether the story you tell makes more rational and economic sense than the mandatory alternative hypothesis "I'm hoping I can find illicit work in Europe since my long-term economic situation at home is hopeless". If you have demonstrated that you're someone who can spend the cost of a hotel stay without squandering your life savings to a degree that a genuine tourist wouldn't, nobody cares if you actually do that.

In particular, once you're in, all you will really be held to is leaving again by roughly the time you said you would (and in any case before your visa expires).

Could you can do it? Yes, you can. Should you do it? I am not not sure, my advice is being honest.

I know that in Portugal, a legal Resident can write a letter saying that you will stay with their and you are their responsibility. I believe the same rule could be applied for Germany.

I will use this approach with my parents next month.

Here there are some explanations: Invitation Letter

One very common reason people travel to the Schengen area is to visit relatives or friends. This is also seen as a visa for tourism in the particular country. So for the invitation letter for tourist visa, family or friends must write it for you. The letter must state that you are the person’s relative or friend and that you are going to visit for a specific period of time.