how to protect 'read more' post content

Hello, I would like to know how to protect some part of the post content automatically (without using level shorcodes like [level-level-3] )

The list of posts it’s ok ( , but when you click ‘read’ more on a specific post, in the post page I want to see the same short text as in posts list, and instead of the ‘read more’ link, the subscription link.

Is there a way to configure this without using shortcodes in every post ???

thanks in advance