i did mine. tape a square around the 135i as well is lines to show where each letter will go so you can line it up again after.
take it off by cutting through the old 3mtape behind it with thread or dental floss.
clean all the old 3m off the back of the emblem as well as the trunk
spray the emblem with PLASTI-DIP (its rubberized paint and works really well, it wont chip, get it at home depot)
reinstall with new 3m adhesive tape.