If you change the price to free, then people who download without paying will not get a Steam key. They will have to pay some amount in order to get a Steam key. (Our minimum allowed payment is 50 cents) Does that work for you ? Or do you want to set a minimum price on the Steam key
The more I think about it , the more I would like to see a custom threshold price for the External Key distribution. 50 cents is fine for my old games, enough to probably deter key resellers. But for my game-in-progress, a higher minimum would let me attract more players/testers during development while still attaching a 'Retail Value' to the game.
Maybe something similar can already be accomplished with the Refinery tools? I did experiment with a crowd-funding style reward system when I first posted Gravity Garden on Itch, but I've failed to generate much buzz. Maybe too early in development, poor marketing, not enough interest.
I did switch my VR games,Crashed Lander and Chunky Orbits, to Pay What You Want with a bonus Steam key. See if I can generate some buzz. If it goes well I might consider something similar for Gravity Garden.