How to pass custom actions as response for a retrieval intent like ChitChat?

At the moment you can’t do it.

I try to have rule with full retrieval intent (eg: faq/location) and custom action in rule.yml.

- rule: Respond to FAQ location
  steps:
  - intent: faq/location
  - action: action_location

When run rasa data validate it show:

rasa/shared/utils/io.py:97: UserWarning: Issue found in 'data/rules.yml' while parsing story rule:
User intent 'faq/location' is a full retrieval intent. Stories shouldn't contain full retrieval intents. Rasa Open Source will only use base intent 'faq' for training.

You could think about custom actions begin with utter_. But It won’t work either because as mention here

Stories and written like for regular responses, but instead of starting with utter_, custom action names should start with action_.