Should we forceNew when the API does not support the operation?

Terraform
#1

We have a use case where a field ‘plan’ in UI can be modified. But the same cannot be done using API.

So while developing the resource we have made the field as below,

"plan": {
				Type:        schema.TypeString,
				Required:    true,
				ForceNew:    true,
				Description: "plan",
			},

But since the field is ForceNew, we have a serious confusion whether to use ForceNew or not. If we use ForceNew, our resource will be deleted and created as new resource, which is a deviation from UI functionality, where in the UI field plan can be updated without creating a new resource.

Now my question is, should we continue to use ForceNew and create new resource. Or should we set ForceNew: false, and prompt error to user when he tries modifying the field saying this field modification is not supported yet.