It would be really helpful.
Something like:

#  mixin.bugfix.concurrency=true

Or:

#  mixin.bugfix.concurrency # Default: true

Note in the second one there is a # so that when you uncomment the beginning of the line, it doesn't uncomment that text

The issue with these approaches is that if a modernfix update changes the default, it would be impossible to know. In this case, modernfix should update that text automatically to whatever is correct.

I've added something along these lines in 5.4.0.

Thank you!