Legal analysis: The content of the contract can be changed after the house purchase contract is filed, but the corresponding conditions must be met. It can be settled through negotiation with the developer, and the buyer and seller negotiate voluntarily. The terms and content of the contract can be added or modified with the voluntary consent of both parties. If a contract that has been canceled or modified has been registered as mortgage, the mortgage registration must be canceled first. A contract that has been canceled or modified must carry the original and copy of the mortgage cancellation document.

Legal basis: "The People's Republic of China and the Civil Code"

Article 543 The parties may modify the contract if they reach consensus through consultation.

Article 490: If the parties conclude a contract in the form of a contract, the contract shall be established when both parties sign, seal or fingerprint. Before signing, sealing or fingerprinting, one party has performed its main obligations and the contract is established when the other party accepts it. Laws and administrative regulations stipulate or the parties agree that a contract should be concluded in written form. If the parties do not use written form but one party has performed its main obligations and the other party accepts it, the contract is established.