at the beginning the rally boys reshelled their sierras into escort shells and were allowed to keep the sierra reg but dont think you can do it now.
it looks like a ringer to me,should be on a Q if anything.
sometimes if you did it over a period of time say changing say engine then changing logbook at dvla then changing colour then shell ...everytime changing it on logbook and returning to dvla you could change full car eventually...but again you cant do this now to the same extent.......not that i have ever done any of the above