Graft being like magic items that could work in any of this forms:
get a bonus and a lesser penalty related to the type of graft.
get a bonus and a lesser penalty related to the type of graft unless you have a feat.
you can have a total of grafts equal to your CON modifier
you can have a total worth of grafts equal to your CON modifier (the worth of a graft is a property to balance how many graft are allowed)
you can have a total of grafts equal to the graft feats you have taken.
aditionnal (one, both or depends on graft)
the graft replaces a limb (game impact) or a neutral bodypart (without game impact like eye, mouth, lungs, etc)
the graft is in adition toy your caracteristics
The grafts are acquired or removed only in a shop (like the tattoo shop) and might require to bring a specific item in addition to the price (like dragon wings, ogre arms, aboleth head, etc)
Undead Florida could be the place for this shop