Is it illegal to break the custom?

But it may be suspected of fraud.

note:

Fortune-telling is not illegal and does not harm social and national interests. However, if you encourage others to commit crimes or infringe upon the social interests of others and the country, it is a crime and constitutes a joint crime. If he slanders you, it is actually a violation of your personal rights. However, according to China's laws, only those who cause harm will be investigated for civil liability, otherwise it will not constitute a crime. I suggest you refer to the general principles of civil law. This is actually not illegal.