I can see Topix deleting a,post ..But NOT changing it ..why would they bother
It is possible, and we assume that they would not.
It is more probable posts are rewritten by people to deceive. It is a rather easy thing to do. It has happened to me. I confronted the individual, and they disappeared from Topix.
That is why you should be careful in what you write, so that it makes sense to you. If you notice a rewritten post, that doesn't make sense, you can go back and find the original. Also you can complain to Topix, and they can/might do something about it.
I am reminded of Kruschev in the USSR, "releasing" documents about Pius XII, after his death, in order to undermine his work. The documents were later found to be lies, but the effect of this set of lies deceived many, and still do so today.