You can include a remote kustomization.yml file but not a single value. You could build your own transformer plugin if you really wanted to, but it's not really in the spirit of Kustomize.

Usually with kustomize what you are going to use is an overlay and patches (which is one or multiple files) that are kind of merged into your base file. A Patch overrides an attribute. With those two features you predefine some probable manifest-compositions and just combine them right before you apply them to your cluster.

You can add or edit/set some specific attributes with patches or with kustomize subcommands like so:

kustomize edit set image your-registry.com:$image_tag

# just to identify version in metadata sections for service/deployment/pods - not just via image tag
kustomize edit add annotation appVersion:$image_tag
kustomize build . | kubectl -n ${your_ns} apply -f -

But if you want to have a single manifest file and manipulate the same attributes over and over again (on the fly), you should consider using helm's templating mechanism. This is also an option if kustomize does not allow you to edit that single specific attribute you want to alter.

You just need a values.yaml file (containing key/value pairs) and a template.yaml file. You can pre-set some attributes in the values.yaml - on demand you can override them per CLI. The tool will generate you a k8s manifest with those values backed in.

template file:

---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: {{ .Values.appSettings.appName }}
  namespace: {{ .Values.appSettings.namespace }}
  labels:
    name: {{ .Values.appSettings.appName }}
spec:
  replicas: 1
  template:
    metadata:
      labels:
        name: {{ .Values.appSettings.appName }}
    spec:
      containers:
        - name: {{ .Values.appSettings.appName }}
          image: "{{ .Values.appSettings.image }}"
          ports:
            - containerPort: 8080
[...]

---
apiVersion: v1
kind: Service
metadata:
  name: {{ .Values.appSettings.appName }}-svc
  namespace: {{ .Values.appSettings.namespace }}
  labels:
    name: {{ .Values.appSettings.appName }}
spec:
  ports:
    - port: 8080
      targetPort: 8080
  selector:
    name: {{ .Values.appSettings.appName }}

Values file:

appSettings:  
  appName: your-fancy-app
  appDomain: please_override_via_cli
  namespace: please_override_via_cli

CLI:

helm template
  --set appSettings.image=your-registry.com/service:$(cat versionTag.txt)
  --set appSettings.namespace=your-ns
  --set appSettings.appDomain=your-domain.com
  ./ -f ./values.yaml | kubectl apply -f -