Jenkins Helm - use existing security realm, not overwritten by helm

Jenkins setup: Kubernetes Debian GNU/Linux 11 (bullseye), image jenkins/jenkins:2.346.1-lts-jdk11 helm chart version: 4.1.10

We’re trying to migrate an old Jenkins instance into a new cluster, and want to retain all settings where possible. I have mounted Jenkins_Home successfully, however I think the jcasc settings are overwriting the security realm (and maybe more) in the imported data. The old instance was not managed by Helm.

Is there any way to turn this off in the helm chart, so the imported settings remain active?