How to modify a manifest file when using Ansible to install a service on a kubernetes cluster?

I am trying to automate making a HA cluster with Ansible.

Normally I have two options to install the load balancer (MetalLb), with manifest or helm.

I really like that helm has a --values option. This is useful because I can add toleration to the MetalLB speakers, that way I can deploy them in the nodes that I dont want to deploy jobs on.

When making the playbook I want to have a way to deploy the MetalLB speakers with the toleration so they can get deploy but I don't want to install helm on one of the nodes.

When the playbook is ran I can download the manifest file https://raw.githubusercontent.com/metallb/metallb/v0.13.7/config/manifests/metallb-native.yaml but now I want to be able to add the tolerations. How can I accomplish this without me downloading the yaml file and editing it myself, something like the --values option in helm would be nice

https://kubectl.docs.kubernetes.io/references/kustomize/kustomization/ lays out the general idea of how kustomize is going to work: take some bases, apply some transformations to them. In most cases, the strategic merge behaves like folks expect, and is how the kubectl patch you mentioned behaves¹. But, dealing with array values in merges is tricky, so I have had better luck with using JSON Patch array add support, which is what we will use here

# the contents of "kustomization.yaml" in the current directory
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- https://raw.githubusercontent.com/metallb/metallb/v0.13.7/config/manifests/metallb-native.yaml
patches:
  - target:
      version: v1
      group: apps
      kind: DaemonSet
      namespace: metallb-system
      name: speaker
    patch: |-
      - op: add
        path: /spec/template/spec/tolerations/-
        value: {"effect":"NoSchedule","key":"example.com/some-taint","operator":"Exists"}      

Then, using kubectl kustomize . we see the result from applying that patch:

      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/master
        operator: Exists
      - effect: NoSchedule
        key: node-role.kubernetes.io/control-plane
        operator: Exists
      - effect: NoSchedule
        key: example.com/some-taint
        operator: Exists

Obviously if you wanted to wholesale replace the tolerations, you may have better luck with the strategic merge flavor, but given that your question didn't specify and this case is the harder of the two, I started with it

FN 1: I saw you mention kubectl patch but that is for editing existing kubernetes resources, so after you already deployed your metallb-native.yaml into the cluster, only then would kubectl patch do anything for you. Using kustomize is the helm-replacement in that it is designed for the manifests to go into the cluster in the right state, versus fixing it up later