The pivot approach is a good one if you can make it work. The below method is my standard for similar situations.
Here is an example of the dictionary rule node approach that was mentioned earlier in the thread.
There is a second one below it that targets specific rows for changes as well if that is necessary for you use case.
You can use this approach to create one combined formula change list and then apply them with a single dictionary rule node as long as they are in the same order as your series of joins.