How did you do that

I'm interested in learing how ABCreator works and have been looking at how the AB40K datafiles have been put together in order to learn by example.
I mostly get it, however, one thing is bugging me and I was wondering if someone can tell me how it works?
Some units (chaos space marines & ork boys for example) have the squad leader replacing one of the normal guys. AB does not directly cater for this as far as I can tell. Instead you use a stat to store the actual number of models in a unit (i'm guessing this was originally used to work out if a unit fits in a transport) and call the procedure gnTrnSpace to update this stat.
But how is the actual maximum of the parent unit changed. I can't find a call to do this anywhere.
Thanks in advance.
I mostly get it, however, one thing is bugging me and I was wondering if someone can tell me how it works?
Some units (chaos space marines & ork boys for example) have the squad leader replacing one of the normal guys. AB does not directly cater for this as far as I can tell. Instead you use a stat to store the actual number of models in a unit (i'm guessing this was originally used to work out if a unit fits in a transport) and call the procedure gnTrnSpace to update this stat.
But how is the actual maximum of the parent unit changed. I can't find a call to do this anywhere.
Thanks in advance.