We're a hosted customer on FusionAuth 1.54.0, and want to add a custom url to have a total of two.

My question is: since we have to replace the existing custom url with itself and the new url, and we didn't already have a CNAME in-place for the original url, will this cause a DNS outage until we get the CNAMEs in place for both urls, or is there an 'activate' feature after we input the custom urls and click Submit? The goal is to have no downtime if we're able.