update-account-password-policy for Organisation level

I believe that can only be done in account level, but you can complement with other approach such Single sign on (SSO) https://docs.aws.amazon.com/singlesignon/latest/userguide/useraccess.html.

And you can still use IaC to automate it during account provisioning. For instance in Terraform you will you https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/iam_account_password_policy