that the spell in question? poppets are meant to represent that person. you make the doll in their image, and [hopefully] incorporate things of theirs into the doll [like old clothes, picture, hair, blood, necklace, so on] this charges the doll to their energy and work used with this poppet would be cast over the person. a spell cast using a poppet of another would be cast over the person, not the poppet. [actually, yes, it's cast on the poppet and the poppet is now enchanted, but the spell is effecting the person the doll represents. this is how voodoo dolls work]
the spell, i'm iffy about with the destruction of the item. if i were you, i'd add a chant to it just to be safe. state you want [persons name] to be broken of [habit] but no harm to come to them. yes, the items you anoint the poppet with have protective qualities, it's better to be safe than sorry. as well, visualize the outcome.