How many different processes will modify your file?
Would templates work for you?
What about this:
- name: grab value of line DirctoryIndex
shell: grep 'DirectoryIndex.*index.php' /etc/httpd/httpd.conf
register: DIline
- name: comment out DirectoryIndex
lineinfile: dest=/etc/httpd/httpd.conf regex='DirectoryIndex' line="# $DIline.stdout"