Yes, you can use the Read More filter: https://codex.wordpress.org/Customizing_the_Read_More#Modify_The_Read_More_Link_Text
Per the discussion below, in this case, there’s a plugin called Page Links To that may solve your problem. You would create a post in WP but set its permalink to the external URL you want to link to, so it would appear on the front page but its read more button would go to the external URL for just that post (or however many others you created this way).