the chassis code for single cab & double cab is different.
there is no restrictions for buying of single cab or double cab 4x4 or 4x2
the chassis / frame of every pickup truck be it 4x2 or a 4x4 has identical DNA. That means cab & loading tub can be swapped as bolt-on change. specific to Hi-Lux low end to top end variants as in Champ/Revo/Roko/Choco/Kupoo/Nuboo /Fanta/ Pakola etc etc
in order to know what exactly you wish to achieve you shall spend some time physically inspecting the variant you have and what you desire it to become.
Then visit RWP kacha stop and look for desired Cab & Tub,
2nd place for such swaps is Kala Dhaka close to Mianwali.
under prevailing circumstances it may require quiet a good fortune approx 35% of the vehicle value and the vehicle will lose, higher value at resale for being illegal swap.
Over the registration papers & govt registration database it will be the same variant as registered under frame & engine number.