Oh thank you, I'm sorry for being afflicted with textual anxiety lately. It can feel that one's words aren't quite right. Your idea of angels changing shape has been in my mind- I had forgotten that Jesus changes shape. I even uploaded a paper on it some time ago.
I started to wonder if Tamar's disguise might be a suggestion of a changeable body—then if the makeup & cosmetics that the Watcher's wives are known for, might be a suggestion of polymorphy.
Why does God change the names of some people? Sarai/Sarah is the only female. She shifts states somehow. I do think her theme is sexual pleasure, the acceptance of the human man, and of human embodiment.
The great problem of the Bible is this problem of spirit placed into an animal form, a strange hybrid being called the human.