There is somewhat similar answer in the below mentioned link:
Removing any and all inline styles from the_content()Removing any and all inline styles from the_content()
where some inline style are being removed with the help of preg_replace and wordpress hooks (wp_insert_post_data & the_content).
Similarly any part of the content can be modified with the as the same done in this (Removing any and all inline styles from the_content()Removing any and all inline styles from the_content()) case.
