Converting a style sheet is a little more involved than using a global search and replace to convert left to right, and vice versa. While this may catch many of the things that need changing, it won’t catch all, and it could also introduce errors into the style sheet.
For example, I had selectors called .topleft and .bottomright in my style sheet. These, of course, shouldn’t be changed. There may also be occasional situations where you don’t want to change the direction of a particular block.