No. You need to define the value for FILENAME_DEFINE_PRICING to be whatever you named the file to be.
It's just a pattern. It's not complicated.
Here, I'll spell it out for you:
In the About Us addon, there are numerous files which you rename and whose contents you adjust to match whatever new name you're trying to create.
You renamed the /includes/languages/english/html_includes/define_about_us.php file to something else, right?
And in the /includes/extra_configures/about_us_filenames.php you renamed FILENAME_ABOUT_US to FILENAME_PRICING and changed its defined value to 'pricing'.
But you somehow skipped changing FILENAME_DEFINE_ABOUT_US to FILENAME_DEFINE_PRICING, and to actually set its value to 'define_pricing' (or whatever the name of the define-page is that you gave it.
Until you define it, that reference in the header_php.php file to FILENAME_DEFINE_PRICING will just keep saying FILENAME_DEFINE_PRICING, thus making the output never show up, and just generating more error messages.
You have to follow the pattern completely, not selectively.