is that possible to change default behavior for contact creation

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i have first name and last name on my chat launch form, I initiated couple of chats without email address and every time chats created under [email protected] email address and system is not creating a separate contact each time. all chats adding to one generic contact. is that possible to to add a custom field as an unique identifier and create separate contact for each chat on the basis of custom field. or what is the better solution to handle this situation.