Can I do an array append using HelmChartConfig with a manifest file for RKE2 (i.e. https://docs.rke2.io/helm/#customizing-packaged-components-with-helmchartconfig)? Specifically I'd like to add the

--default-ssl-certificate

argument to

rke2-ingress-nginx-controller

config to spec.template.spec.containers.args array as an append so that all the default arguments are still there without me specifying (as I've noticed they change between versions at times). I know I can replace a value, but it isn't clear if I can specify an array append to what's there in a generic fashion.

No, I don't believe Helm lets you merge/append lists like that. The Chart and ChartConfig values are literally just passed into helm as values files, it handles all the merging itself.