I shifted to Chennai from Gurgaon close to a year ago...MY car has a HR registration.
Since I wasn't sure how long I'll be in Chennai (I knoew that it won't be for too long) I didn't want to get the car re-registered here
(it may be illegal but I am in a mobile career...I really don't want to be shifting my registartion no every year or two)
Anyway, theoretically, you don't need a re-registration if you are in a different state for a transitory period of 6 months..I carry a copy of that clause from the Indian MVA in my Glove, and Fortunately, I have never had any issues with the car bearing a HR number...
I have been fined a couple of times here (For driving outside the center lane on Mount road , the main thoroghfare in chennai...they have a funny rule on lane discuipline on parts of Mount road
) but have never been hassled for the registration number
I don't want to advise you to do the same, assuming you are moving to Chennai for keeps...Just thought that I'd share my perspective too