@saint 

Refer below knowledge article,

https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0547597

You can use preserve and exclusions during cloning,

https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0717012

Cloning does not overwrite the email settings of the target instance although it does disable email and would need to enable email.

You can use manual method or automated script to maintain post-clone changes.

If this helped to answer your query, please mark it helpful & accept the solution,

Thanks,

Bhuvan