Configuration Best Practices 

Use a Sitepackage extension 

It is generally recommended to use a sitepackage extension to customize a TYPO3 website. The sitepackage contains configuration files for that site.

See the TYPO3 Sitepackage Tutorial on how to create a sitepackage. We assume here your sitepackage extension has the key my_sitepackage.

The YAML preset files should be kept in folder EXT:my_sitepackage/Configuration/RTE/.

RTE configurations need to be registered in your sitepackages ext_localconf.php:

$GLOBALS['TYPO3_CONF_VARS']['RTE']['Presets']['myconfig']
    = 'EXT:my_sitepackage/Configuration/RTE/MyConfiguration.yaml';

Use TYPO3’s Core Default.yaml as boilerplate 

It is recommended to start by copying the file typo3/sysext/rte_ckeditor/Configuration/RTE/Default.yaml into your sitepackage to the file EXT:my_sitepackage/Configuration/RTE/MyConfiguration.yaml.

Check TYPO3's Core Full.yaml to gain insight into a more extensive configuration 

This preset shows more configured options and plugins. It is not intended for real use. It acts as an example.

typo3/sysext/rte_ckeditor/Configuration/RTE/Full.yaml

Use Core includes 

It is recommended to use the following includes at the top of your custom configuration:

imports:
  - { resource: "EXT:rte_ckeditor/Configuration/RTE/Processing.yaml" }
  - { resource: "EXT:rte_ckeditor/Configuration/RTE/Editor/Base.yaml" }
  - { resource: "EXT:rte_ckeditor/Configuration/RTE/Editor/Plugins.yaml" }

If you started out by copying this extensions Default.yaml as boilerplate the imports should already be there.

The include files are already split up so the processing transformations can just be included or even completely disabled (by removing the line for importing).