So I searched for some codes but all I found is about how to read some sectors and bits and blah blah.
The code for rewriting first writes something you want and then reads it. Soon I am going to a spa hotel and I want to read their cards's info stored (especially for my friends's cards in order to troll them :D) and then write it over my own card (which is now empty). How can I do this?
The device I am using- RFID RC522
It is unlikely that any information is stored on the card (although I could be wrong). Each card has a unique ID and it is this that controls what someone can or cannot access.
In theory you can't change the embedded card ID. In practice I believe that it is possible to clone a card with specialist equipment, but that is beyond my interest in the subject.