If you want to change something about Reach, you should do it through the child theme.
A child theme is simply a theme that inherits the functionality and looks of another theme – the parent. The whole idea of a child theme is that you can modify, and add to the functionality of that parent theme without modifying it directly.
By using a child theme you don’t need to worry about losing your modifications when you update WordPress or your theme. Only your parent theme is updated – your child theme remains intact.
Using the Child Theme
Using a child theme is no different from using any other theme. From your WordPress Dashboard, navigate to Appearance > Themes and set your child theme to Active.
Then you can work with the theme as you normally would.
To override a Reach template, you need to create a copy of the template file in the same location in your child theme.
For example, if you want to override the template that adds the login and profile links to the header, the template you need to override is
partials/account-links.php. In your child theme, you need to create a file at
partials/account-links.php — you can copy and paste the contents of the original template into your child theme’s version and modify it however you want.