Unable to use the same custom domain on two services

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**Tell us about your request**
What do you want us to build?

Here's our challenge: we have a production App Runner service that has the Custom Domain `*.example.com`. This uses the "build from code" build process. We need to change this to "build from ECR". We can't update the service in-place, so we have to create a new App Runner service. We can build the new service, but we can't add the domain name `*.example.com` to this new one.

How do we migrate from service A to service B with zero downtime? We were intending to get it set up and ready to receive requests, then simply re-route the DNS. This seems impossible without deleting service A - incurring downtime - then quickly adding the domain name to service B and praying ACM validates it quickly.

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

No alternative available for reusing the same domain name when creating a new App Runner service.

**Additional context**
Anything else we should know?

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