Andrew,
Thanks for your sincere engagement with particular parts of my book, and for making points that at least implicitly interact with my propositional argument laid out in my original post. I need to say at the beginning though, I am not 100% certain on what you mean by your many uses of "culture" in your expressed thoughts.
1. Regarding positive worship and the RPW
My phrase "positive instituted worship" falls under the Confession's phrase in 1.6, "The whole counsel of God concerning all things necessary for His own glory, man's salvation, faith and life;" therefore it must be "either expressly set down in Scripture, or by good and necessary consequence may be deduced from Scripture".
I am speaking of what is formally positive worship, not what may be considered materially positive worship. Take for example prayer: spiritual prayer is formally worship to God. Yet the material actions of praying, in this or that posture, location, dress, time, aloud or silently in the congregation, etc. etc. are circumstantial and are to be ordered by nature's light, Christian prudence and the Word's general principles. Rutherford makes this distinction and similar ones in Divine Right (1644), pp. 3-5.
Hence I agree with you that not all material aspects of worship are either expressly set down in Scripture or may be and are to be deduced therefrom, especially what you underlined.
Corinthian head-coverings were a circumstance of their worship common to society around them.
The final phrase in 1.6, "which are always to be observed" refers to the "general rules of the Word". It does not make sense with the whole previous thought as its only "some circumstances" which are in view, and though some of them are "common to... societies", they need not be universal to all societies (as head-coverings).
I affirm that circumstances are sometimes in themselves indifferent.
2. On cultural issues.
I agree that the Church, or a church may have its own culture in some sense different from the outside society. "Culture" is a very ambiguous term. If I might try to pinpoint the most accurate way of defining the issues (as I did in my book), the fundamental issues (as Rutherford defines them in Divine Right), even more so than "culture", is whether head coverings are justified by the light of nature (including secondary laws of nature, involving society and culture), or whether they are not, and are positive above the light of nature.
I agree in some sense it may be said that a Church may have a certain culture distinct from the world insofar as it orders government and worship according to nature's light, Christian prudence and the Word's general rules, which may change over time, as you say. You use the words that the Church may "determine" and "prescribe" such, which goes beyond the Confessional language of "order". I don't know if we understand those things the same, as the Church's authority to bind those things only goes so far as those principles are inherent in the circumstances themselves, and not a degree higher. Hence the Church cannot artificially bind such things where the light of nature, Christian prudence and the Word's general rules do not.
It is possible that at times certain elements of Church culture are quite similar to those of the world around it.
As far as all this being justification for it being warranted for women to cover (or be required?) to veil in Church, when the culture does not: I deal with that in the book in various places for the Corinthian context, and argue that it de facto was not legitimate for what Paul was describing in 1 Cor. 11; see the top lines of p. 69, p. 125 point 8 with the footnote, p. 228 point 10 and possibly other places.
Could women legitimately veil from the light of nature and culture (perhaps a church culture) when the larger outside culture generally does not? It has been put forward that though women do not generally veil in America, yet it may be appropriately done in Church as that is a more formal setting, similar to how a man does not anymore generally wear a tie in public all the time, but may legitimately for Church. On that paradigm, yet women would then expect to veil for other more formal occasions outside of Church, such as where men wear ties. If that never happens, then I don't see how women veiling is actually a common circumstance of society or truly tied to the formal setting (but rather is just a pretext to veil in Church, making it positive, above the light of nature, formality and culture).
For a church culture to be completely distinct from society's culture simply makes that church culture to be positive, and we are back at the same issues I argue in my book: one can't just make things up beyond the light of nature or what is common to culture, as only God can institute legitimate positive things above the light of nature, He being the sovereign Creator over it.
3. Mutable apostolic ordinances
See pp. 38-42.
4. Church culture requiring and cultural warrant
You asked, "can it not be that the culture of a church or congregation is one that would require head coverings?" A church cannot require such if it is not required by Scripture or the law of nature (including the light of nature and circumstances common to society) or Christian prudence. Note in 1.6 it only speaks of the Church ordering its own worship and government according to these things and the general rules of the Word; it does not say it can require them of others or church members. It takes particulars to do that, which is beyond the general rules of the Word. See pp. 96-102 on the topic of a Church claiming to require something above and beyond Scripture and the light of nature.
As far as what is warranted in a culture, that is taught by the light of nature (empirical observation, etc.). That may be observed by all people, as all have the light of nature before them. That should be a ground of union, not of division, if such practices are clear from the culture. If they are not clear, then it may be a ground of division, or at least various practice, and for a church to impose uniformity on it when the culture is not uniform, that is not only unwise, but it is unwarranted.
I'm sorry perhaps I am not answering all your specifics (due to time and energy). Your fundamental premise seems to be the Church using head-coverings in its own culture when such is not a common circumstance of society. I would submit that that is contrary to WCF 1.6.
If you do not agree with the conclusions of the book, I understand, but I think nonetheless, you may derive a lot of benefit from the related material in the book. I hope it may be of benefit to you in some way.
Blessings friend.