Preview app - add 'rotate slightly'

Is it simply not possible to add functionality to Preview? It's good, handy, useful little app. I like that it's light. But just a couple of more possibilities, and i would not have to look to any other app for just those few things.

Above all: slight rotation, of a few degrees or so. I use PDFs to read music, and very often those pages are sliiiightly out of horizontal. I wish i could adjust them just a little bit.

I know i can spin the image using two fingers on the trackpad, and the image will spin slightly. But this change does not stay, unless you go to 90 degrees, which seems to be only the same as ctrl-R.

C'mon Apple! You can do it! It's an idea whose time has come.