Duplicating lines and other Emacs miscellanea

A few weeks ago I wrote about how I remapped yank to my command which allows to transform the yanked text. The whole setup – where I press C-y twice to trigger the transformation transient – has one drawback: I sometimes legitimately want to call yank twice in a row. This happens when I need to copy the current line and modify the copy so that I have two similar lines in a row. (I often need this when editing Ledger transactions, for example.) What I sometimes do in such a situation is basically a dance of C-a C-1 C-k C-y C-y. It turns out I don’t need to.