I know it’s an old thread, but for future ppl finding this thread.
The only way I found out to easily and quickly change parent class of components within blueprints, is by copying the component to notepad or other text editor, change the class here in the XML like structure to a child class you created. Just find and replace the text string that defines the component. I had to do it twice on each component, Once in ‘Begin Object Class’ and once in exportPath.
When those 2 strings are changed, copy and paste the component back to your blueprint, but make sure you delete the original component first.
And voila, your component now inherites your custom subclass.