I usually add a message field type and change the message with the acf/load_field filter:
function rosters_away_message($field){
$field['message'] = "<button style='color:white; background-color:beige' type='button' class='btn btn-success btn-sm'><a target='blank' href='http://'>Add new</a></button><br /><br />".$roster_final;
$field['label'] = " ROSTER";
}
return $field;
}
add_filter('acf/load_field/key=field_5929a3d8a859c', 'rosters_away_message');