Whether you change the whole tailgate or just the glass if you use one from a face lift model you will either have to use the later spoiler or modify your original one as the position of the outer mounting hole are in a different position. Basically the spoiler is mounted on the Glass hinges not the main tailgate hinges so it is not really necessary to change the whole tailgate. Ideally if you could get a two piece tailgate complete with spoiler it would be a straight swap. Obviously it would need to be from a Autobiography to get the right style spoiler to match the HST.

Cheers
Col