It is undoubtedly illegal to replace the wholesale clothing with your own hang tags and collar tags.
First of all, if a clothing trademark is not registered, it cannot be sold with a hangtag or a ticket. The act of adding a hangtag or collecting a label violates the relevant provisions of the trademark.
This behavior also infringes upon other contract law rights of the clothing manufacturer and should be punished by the industrial and commercial department in accordance with the law.