Well it's changing the size based on selection that's difficult for me, that doesn't also apply attribute bonuses or penalties. Also making it so you can only select small or medium. I don't own Bestiary 5, only the first bestiary and a few select content bits, as I'm poor and all that. I have Rbook Entry Path, Advanced Player's Guide, Ultimate Magic, Summoned Creatures, Bestiary 1, Campaign Settings #9 and 12, and Iron Gods encounters.
I think a better way to do this than a selector might be alternate racial traits, like the way the tiefling hertiages work. It will default to small, since most of them are small, but you can select a medium variant which increases your speed but you lose out on a single racial ability (double checked, skilled climber is only for small).
But again, changing the size without messing with the ability scores. How do I script that?
EDIT: Freeport, City of Adventure Saves the Day!
Some island trolls, whatever those are, can be large sized instead of medium. Well, with this code, I can make the alternate racial trait for small to medium!
Code:
doneif (tagis[Helper.SpcDisable] <> 0)
hero.findchild[BaseRace].field[rSTR].value -= 2
perform hero.findchild[BaseRace].tagreplace[RaceSize.Medium0,RaceSize.Large1]
~ hieght/weight adjustments
hero.findchild[BaseRace].field[rHeightMnM].value = 90
hero.findchild[BaseRace].field[rHeightMnF].value = 87
hero.findchild[BaseRace].field[rWeightMnM].value = 375
hero.findchild[BaseRace].field[rWeightMnF].value = 340