How to replace some of the values in Helm template definition? - kubernetes-helm

Question

I have a value someField in my values.yaml file that looks like this:
someField:
field1: 1
field2: someValue
field3: someObject
...
I now want to add this to my template, but change some of the fields and add some other fields and maybe remove some of them too.
someField:
field1: 2
field3: someObject
...
field100: someNewValue
I can write to my template all the fields one by one and then do what I want, but there are multiple fields that are available and I would like to avoid listing them all.
I can use toYaml, but it would fully write the original value, and I do not know how to augment it "on the fly"
Extended example:
I have another helm chart installed that is called KEDA, and it defines a CRD:
apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
name: {scaled-object-name}
spec:
scaleTargetRef:
apiVersion: {api-version-of-target-resource} # Optional. Default: apps/v1
kind: {kind-of-target-resource} # Optional. Default: Deployment
name: {name-of-target-resource} # Mandatory. Must be in the same namespace as the ScaledObject
envSourceContainerName: {container-name} # Optional. Default: .spec.template.spec.containers[0]
pollingInterval: 30 # Optional. Default: 30 seconds
cooldownPeriod: 300 # Optional. Default: 300 seconds
idleReplicaCount: 0 # Optional. Default: ignored, must be less than minReplicaCount
minReplicaCount: 1 # Optional. Default: 0
maxReplicaCount: 100 # Optional. Default: 100
fallback: # Optional. Section to specify fallback options
failureThreshold: 3 # Mandatory if fallback section is included
replicas: 6 # Mandatory if fallback section is included
advanced: # Optional. Section to specify advanced options
restoreToOriginalReplicaCount: true/false # Optional. Default: false
horizontalPodAutoscalerConfig: # Optional. Section to specify HPA related options
name: {name-of-hpa-resource} # Optional. Default: keda-hpa-{scaled-object-name}
behavior: # Optional. Use to modify HPA's scaling behavior
scaleDown:
stabilizationWindowSeconds: 300
policies:
- type: Percent
value: 100
periodSeconds: 15
triggers:
- type: service-bus
authenticationRef: name-of-auth
I have my own HelmChart where I want to generate this CRD from a definition, but change some values.
So a user would provide spec, but I would augment it by e.g. adding 'authenticationRef' to every element of the triggers array.