You mean you want to change the right side crank case.....yes its possible i think it's for Rs2500 for side.....and 5k for pair....Genuine Atlas Honda....
As far as the legality is concerned you have to go to ETO and submit the following doc....you would obviously have to file for engine change. This list is for punjab only (not sure about Isb aur other provinces)
Now in case of Punjab the below links would be helpful for you
http://excise-punjab.gov.pk/downloads/DOCUMENTS_REQUIRED_NEW_POST_REGISTRATION.pdf
http://excise-punjab.gov.pk/download.html