So what is the need for this? To be honest i personally don't think you should. Instead i would say that you should have an external registry like quay and you push TO it and not the other way around. Using your CI/CD solution.
I can understand that you want your admins to do it from a debug point of view... Good and bad stuff as allways.
oc patch configs.imageregistry.operator.openshift.io/cluster --type=merge --patch '{"spec":{"defaultRoute":true}}'
If you want a shorter image registry
oc patch configs.imageregistry.operator.openshift.io/cluster --type=merge --patch '{"spec":{"routes":[{"name":"image-registry", "hostname":"image-registry.'$INGRESS_DOMAIN'"}]}}'