Proposes changes could have been put in one (or just a few) messages with numbered suggestions. This would make it easier to refer to them. Each could have had a link to the file involved in order to make it easy to look at context. My opinions: 

msg200572 disagree
msg200573 agree
msg200576 agree that one of the two is better
msg200578 disagree, I think, though I might change after seeing context 
msg200579 agree that sentence is bad; 'is' has no subject.
msg200580 compiler is present in 2.7, gone in 3.3, 3.4

msg200583 the original is awkward; the replacement is wrong in that it says 'you must do xyz' and then 'if you do not want to do xyz'. Perhaps something like
"When testing changes that affect bytecode output, remove old .pyc files. On unix, use "find . -name '*.py[co]' -exec rm -f {} ';'". When committing such a change, update the magic number."

For running the test suite, that just needs to be run in /lib of the version being tested.  Or now, just delete __pycache__ directories. The Windows equivalent should be given. Or give a python equivalent using shutil.

msg200584 both are 'correct' on Merriam-Webster and wiktionary sites. Firefox only likes the first. I would go with whichever is used most in our docs.

No comment on last two.