Thanks for the suggestion. Here's big picture what needs to be done for anyone interested to pick this up:

First needs support in the provider here: https://github.com/kbst/terraform-provider-kustomization
Then the variable can be exposed in the module here: https://github.com/kbst/catalog/tree/master/src/_terraform_module

@pst

First needs support in the provider here

To clarify, isn't it already supported in the repo here? https://github.com/kbst/terraform-provider-kustomization/blob/c75a675049a3c88b285dc53600ac7d5b380d5f72/kustomize/data_source_kustomization_overlay.go#L338

So it would just need to be exposed in the custom-manifest module?

Edit:

I would love to pick this issue up too regardless. Let me know if that is possible.

You are right, replacements seem to already be supported in the provider. I guess I lost track myself.

@pst no worries - I'm still willing to contribute to the second part you mentioned above:

Then the variable can be exposed in the module here: https://github.com/kbst/catalog/tree/master/src/_terraform_module

Happy to review your contribution whenever you get around to it.

If you add the variable to the .tf files in src/_terraform_module the changes will automatically be included in all future module versions built. That includes both the ones that bundle upstream like nginx or cert-manager, but also the custom-manifests module.