Haroon bhai, i just know about pajero, and this law does not apply on pajero, you can just swap a gen 2 body on gen 2 chassis without paying any tax, because shape of gen 2 is same from 1991-2000, just minor changes in interior! so if you have gen 2 chassis of 1992 model then if you want to you can swap the body of Gen 2 1994 model, you dont have to pay any tax!
BUT! There is a big BUT!
Color & engine hp should be same as mentioned in book
& the engine number is changed accordingly on the book!