Fabio Gollinucci

It's possible to use EventBridge event "CloudFormation Resource Status Change" to execute code when the CloudFormation stack itself is created. 

This can be done describing the EventBridge event rule for a Lambda function that match the emitted event:

StackEvent:
  Type: EventBridgeRule
  Properties:
    EventBusName: default
    Pattern:
      source:
        - aws.cloudformation
      detail-type: 
        - CloudFormation Stack Status Change
      detail:
        stack-id:
          - !Ref AWS::StackId
        status-details:
          status:
            - CREATE_COMPLETE

The event rule pattern is interpolated with AWS::StackId pseudo parameter reference.

So far the only status change that is reported is CREATE_COMPLETE.

Here a GitHub gist with a CloudFormation (SAM) example template: https://gist.github.com/daaru00/d5443e5de9b25fd7ee637e6d6a22d137