求翻译：除非各方另有约定，对本协议的任何修订或变更均须以书面形式作出并由获正式授权签署本协议的人士代表本协议各方签署且加盖公章后方能生效。是什么意思？

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Unless otherwise agreed by the parties to this Agreement, any amendment or modification shall be in writing and signed by a person duly authorized by this agreement on behalf of the person signing this Agreement and the parties can take effect only after its official seal.

Only if all quarters have the agreement in addition, must make to this agreement any revision or the change by the written form and by attains the public figure who the official authorization signs this agreement to represent this agreement all quarters to sign also behind the capping official seal

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