in reply to
Safely altering the behaviour of heavily used modules
You have probably done this already, but it would be useful to add tests for both the new behavior situation and the old default. Check objects returned for both cases, which is something that may not be done in the current test suite. Check that freezing and thawing close the loop in both cases. I'm not sure what race easily means, but I am sure that you will have to deal with it in your proposal.
Add documentation describing changes and give example code where the new behavior may be useful.