I believe that the 400 uses the T/O threshold for the position shift. That means that if only the landing threshold is displaced it won't have any effect when the TOGA buttons are hit. So if T/O is from the normal position, generally full length, then you don't need to do anything.
If you go to the APPROACH REF page the runway distance that is in the database is displayed. This is a good check.
I must admit that I am only explaining what I do. I just checked my Honeywell manual and it is really quite vague.
I may be wrong, and if so I hope that someone who knows better can elaborate.
Cheers.