Have you ever made changes to the code of a theme or plugin and lost it after updating by accident? It could happen easily if you are not careful. There are child themes and other ways to perform changes to your code without having to worry about losing them. Take Lock Your Updates Plugins/Themes Manager for instance. It is a plugin designed to lock your themes and plugins from being updated.
The plugin helps protect your changes. It also lets you store notes to remember what you have changed. Once you install the plugin, you are going to see a couple of new icons next to your plugins, one of which brings up an area for your notes. To lock a plugin from getting updated, just click on the lock button. The same can be done for themes.
There are many other ways to keep track of the changes you make to your code and avoid losing your updates. This plugin simply helps you stay on the safe side. This is a free plugin.