When in comes to making modifications to a WordPress theme, creating a Child Theme is Job #1.
From the WordPress.org codex:
A WordPress child theme is a theme that inherits the functionality of another theme, called the parent theme, and allows you to modify, or add to, the functionality of that parent theme.
Using a child them allows you to
modify the styling and layout of a parent theme to any extent without editing the files of the parent theme itself. That way, when the parent theme is updated, your modifications are preserved.
The WordPress codex goes on to say
For this reason, child themes are the recommended way of making modifications to a theme.
I had the honor of delivering my presentation on Child Themes to fellow WordPress developers at this year’s WordCamp Atlanta conference. You can view my presentation slides here.
Implementing a child theme in your WordPress site can be as simple as adding a few lines of code to your child theme’s stylesheet or as complex as building custom functions that leverage WordPress’ vast repository of hooks.
Let me hear from you if you have questions about implementing a child theme in your WordPress site.