If you want to change a page layout, the templates of interest are:
Instead of changing the default templates, I recommend that you copy and rename the template. Doing so will ensure that changes you make will not be overwritten by future releases of TalkBack. Example: rename comments-display-tpl.php to my-comments-display-tpl.php
Instruct the system to use the different template by changing the template file name in the configuration settings.
Finally, document your changes. Write down in detail what you changed and keep the document in a safe place to refresh your memory in the future.