It would be difficult to test this fix using a toolbox (AFAIK), as it fixes a certain NetworkManager Wi-Fi configuration. Many other updates have similar impacts on the base desktop.
I would also be reluctant to switch entirely to updates-testing (even briefly), as I wouldn’t be able to know whether any regressions were from this update versus others that are currently in testing.
In terms of rpm-ostree override replace <package>, exactly what string should I use for <package>? Can I have an example for particular update I’m trying to test? I’m sure I can adapt that example to the general case.