Transforming yanked text

Recently I found myself killing and yanking more often than ever. One problem with that is that the capitalization and punctuation of what I have yanked is often wrong. As a (pretty stupid) example, I might see the sentence “This is bad.”, and I might want to write another one: “He thinks that this is bad, and he’s right.” If I use kill-sentence (M-k) or backward-kill-sentence (C-x DEL), I have the whole This is bad. in the kill ring, but what I need to yank is this is bad (with lower-case “t” and without the period), so I need to make both changes after yanking. After several dozen such cases I thought, this is Emacs, I shouldn’t be doing this manually!