Using immutability-helper or spread op to make changes to an object, what is better: repeatedly $set, or $merge only once an object with all changes?

Question

In my state I have a dictionary of a flat object:

export interface INodeVisibility {
  id: string;
  level: number;
  isExpanded: boolean;
}
export type NodeVisibilityDict = { [key: string]: INodeVisibility };

In one operation I need to iterate over a list of modifications and add or update the corresponding entries in the dictionary using immutability-helper library. I wonder what would be the best approach:

1. In each iteration do a $set operation modifying or adding the dictionary entry.
2. In each iteration mutate a "modifications-object" and do a $merge of it only once at the end.

Note the data is normalized. INodeVisibility is declared as an interface but it can be understand as a type because it is used as shown, no more properties added.

I'd vote for the second approach but I want to know what is recommended in this case.