I am not sure about change, but pinning stuff down is definitely still going on. As for Sonja's role, she will have the final say, of course, but she does not obviously pay much attention to what happens here and rarely intervenes. Indeed, she hasn't done much publicly about tp for a while (she actually has a job, for one thing) and so we have to assume that the book is percolating without much of its content being revealed beforehand.
tp phrases are not like Eo's compounds: they have less fixed meanings and are much freer in formation. They do not, in general, mean the same thing in all contexts, but rather serve to point out thing in a given context as effectively as possible. What works to pick out one thing in one context make work to pick another thing in another context, while what the the first first picked may in the second case be picked out by some other expression. This is the chess side of tp, after the checkers of easy rules and the tic-tac-toe of strategy.
tp forms change roles without any external marks (which occasionally leads to a problem) but just by turning up in the appropriate slot. Figuring out what a word means then is somewhat trickier (and I, at least, often go way off base in this area). But there are some general rules which are beginning to emerge for big cases (a noun as a transitive verb, for example) or a preposition as a verb. Hopefully more will be systematized as we go along (and Mato has a corpus to plow through for rules).
But for now, we are all feeling our way, with varying degrees of certainty, and a willingness to try something to see if it flies. Not really scary, but often exciting.