Alright, I made three batches, all the same, carefully measured with scale, and handled the same except for:
- one with different extract and
- one which added 20g flour.
The additional flour made a perceptible improvement in holding shape (edges noticeably more sharp all around the cookie, total spread a tiny bit less), as expected, and only had the slightest difference in mouth feel. I am so pleased the extra flour didn't change the flavor as far as my taste testers could tell. I could taste a difference, but the cookie was still pleasant and soft.
The cookie with only the change in extract made no difference from the original recipe (except flavor). By the way, cherry extract tastes a little like cough syrup - I might not rush to use it again soon.