Edit user page outside of drupal core (user-profile.tpl.php) Drupal 7

Hi everyone

Simply speaking I want to edit the yoursite.com/user page via user-profile.tpl.php and user-profile-item.ptl.php files. For example add extra text to history etc

Editing those files is easy but we can’t do that because its the Drupal core. Copying them to sites/all doesn’t work.

Is there a solution for this? How are we suppose to edit the /user/ page?

Thanks for any answers / tips!

Drupal version: 

Source: https://www.drupal.org/taxonomy/term/22/feed