Keep `subchart` updated from upstream using ship


So, in my scenario I have my application’s chart main chart and then prometheus’ sub chart. The thing that I want to achieve is, some values (for ex server.repository.image) of the sub charts should be changed based on a value (lets say airgapped.enabled) that would be specified while installing main chart.

Now to achieve this what I have done is, pull the prometheus chat locally and make the airgapped.enabled global and based on this global value we can change the sub charts templates to have correct value of server.repository.image.

Now obvious problem with this approach is, how are we gonna make sure that the chart is updated with the upstream, I was thinking if replicated ship would be useful here but from what I have looked into, I dont think ship would be able to resolve this specific requirement.

Because after I get the rendered.yaml file the manifests are not templated anymore, so we have the same problem again how would I be able to change a values based on the value of airgapped.enabled.