Using pulumi, AWS and typescript, I want to create a loadbalancer and route53 entry from the same program. Problem is that the loadbalancer and route53 are in different AWS accounts. How do I change between AWS profiles inside my pulumi typescript program?

You can use explicit providers, where each provider instance has a different account: https://www.pulumi.com/docs/concepts/resources/providers/#explicit-provider-configuration

Great, exactly what I need. Cheers mate