How to Create a Site Specific Plugin
Sometimes we provide you with little snippets of code to add or change a feature of one of our themes or plugins. The best way to implement those changes when they deal with PHP code is to create a Site Specific Plugin. These are plugins which never really update(unless you change the code) but just contain little pieces of code to do small tasks.
In this tutorial we'll show you how to create a site-specific plugin without even using FTP our touching code (other than the code you need to paste!).
Install the Pluginception plugin: https://wordpress.org/plugins/pluginception/
Select Create a New Plugin under the plugin menu options
Fill out the plugin options, be sure to include the word Site Specific in the title so any other WordPress webmaster debugging your website will know that the plugin is a custom one.
Click Create a blank plugin and activate it!.
The page will automatically be redirected to the plugin edit screen.You might get a message like the one below, simply click I understand
Paste the code snippet you received from our doc into the edit area and then click Update File. Notice the activation status at the top next to the plugin file path. If it says inactive then that means you need to activate the plugin from your plugins area after updating the file.
That's it! You should now have a site-specific plugin with the modification from our doc without having to create a child theme or log into your site via FTP