prune-change-sets.sh

#!/usr/bin/env bash

set -e

echo "Starting to prune change sets"

ALL_STACKS=$(aws cloudformation list-stacks --stack-status-filter CREATE_COMPLETE UPDATE_COMPLETE UPDATE_ROLLBACK_COMPLETE --query 'StackSummaries[].StackName' --output text)

for STACK_NAME in $ALL_STACKS
do
  echo "Starting $STACK_NAME"
  CHANGE_SET_NAMES=$(aws cloudformation list-change-sets --stack-name $STACK_NAME --query 'Summaries[?Status==`FAILED`].ChangeSetName' --output text)
  for CHANGE_SET_NAME in $CHANGE_SET_NAMES
  do
    aws cloudformation delete-change-set --change-set-name $CHANGE_SET_NAME --stack-name $STACK_NAME
    echo "Deleted $CHANGE_SET_NAME for $STACK_NAME"
  done
  echo "Finished $STACK_NAME"
done

echo "Finished pruning change sets"

This will delete all failed change sets for all stacks for the account/region it is run in.