Hi @emilyruby and welcome to the forum!
I know the feeling as I've worked with a client that has multiple apps connecting to shopify via Graphql and we need to add transformers to each query.
Something that comes to mind is that you could set up a global function and then in your transformer simply pass data as a parameter. You would still have to call the function in each query, but i guess it is better than copying the transformer every time. And if you have a need to update the transformer, you can do it only once in the function.