WordPress - Creating a child theme
If you don’t want your changes to be overwritten by an update of your theme, or you just don’t want to change the theme’s files, then you could create a child theme, and put the slider’s shortcode, or your other modifications in there instead. Here is how you can do it:
Go to this folder: wp-content\themes\
Create a folder with any name:
Create a style.css file in it, and put this code into the file, where the [parent theme folder name] should be replaced with the folder’s name of the parent theme, for example with twentyfifteen if you want to create a child theme for the Twenty Fifteen theme:
/* Theme Name: Child theme's name Template: [parent theme folder name] */ @import url('../[parent theme folder name]/style.css');
Now you can activate this theme from your backend. Copy the files, you want to modify from your parent theme, and do the modifications. These files will load instead of the parent theme’s files, when this theme is activated, and all the other files will come from the parent.