Recently, KLM decided to adopt Transavia's identifier for its new 737-800s and -900s, i.e. they will be -8/9K2s instead of -8/906s. The reason given by KLM is that the use of the normal KLM identifier/customer code would require more paperwork and (I believe) a different certification process. Just how much more work can this involve. It is after all, almost exactly the same aircraft - same cockpit, engines etc?
(By the way, if Air India ordered the 737-700, would it become the 737-737??)