Present an option in customer transformers to use the existing icons that describe transformer functionality.
This would provide more immediate readability for the intended function of a custom transformer.
For example, a FeatureReader has the database read icon attached to the transformer:
If presented the option, I would use this same symbol on a custom transformer I have that is dedicated to reading files with a loop for re-attempts at reading (for better error handling):
I believe it would read a bit better on the canvas (pun intended) for users.