Having read several of the Runelord books I can provide a little bit more information on exactly what is and isn't possible about the system in DF:
0)If you wish for any dwarf to be able to become a runelord rather then a given caste it might be easier to use food carrying syndromes instead of a boiling stone to enable the interaction. The basic method would be something like:
a)Facilitator makes forcible into a cheese type food item called "rune of _____ forcible"
b)you lock the runelord into a room with the food and the dedicate into an adjacent one with a fortification allowing sight from one into the other
c)runelord eats the food enabling him to steal the attribute from the other dwarf with an interaction
Not exactly the same as the book, but it would allow you to make a runelord out of any dwarf instead of only specific ones. Just make sure not to leave any of that "rune of strength forcible" cheese lying around the dining hall.
1)Right now you can have interactions that edit all of the attributes listed
here, as well as directly change speed (CE_SPEED_CHANGE, which would be closer to a metabolism endowment then agility would be) and luck of a sort (CE_SKILL_ROLL_ADJUST, which can throw a percent modifier onto skill roles).
2)There currently isn't a way to handle vectors, since the game won't track who dwarves have given endowments to. Similarly there currently isn't a way to make a runelord lose their endowment should the dedicate die or the dedicates regain it should the opposite happen. As such all enhancements or decreases of an attribute are permanent unless later canceled out by giving/taking an endowment.
3)You can make it so that dedicates can't give away endowments multiple times (apply a harmless syndrome and then use IT_CANNOT_HAVE_SYNDROME_CLASS to prevent all of the dwarves that have the "dedicate" syndrome from giving an endowment.