BOTOX and BOTOX Cosmetic are exactly the same formulation of botulinum toxin type A (onabotulinumtoxinA); they are manufactured in the same plant, have the same molecular weight, and are packaged as 100 Units of toxin per vial. The differences are not related to marketing, but instead FDA approval.
BOTOX is approved for abnormal twitching of the eyelid, muscle stiffness and contraction in the neck, chronic migraine headaches, overactive bladder due to neurologic disease, strabismus (a condition in which the eyes are not properly aligned), upper limb spasticity, and severe underarm sweating.
BOTOX Cosmetic is approved for moderate to severe frown lines between the eyebrows.
Antibody formation should not be a concern. Many patients are treated with more than 100Units of BOTOX and have no problems. In my practice, some patients receive BOTOX Cosmetic for their frown lines and other facial areas, and also have their underarm sweating treated. These individuals may receive about 120 -170 Units for the treatment of all these areas and have had no problems; this would be similar to what you are asking about.
Be sure to seek an experienced injector who purchases their BOTOX from the manufacturer (Allergan); this ensures you are receiving the genuine product.
Best wishes, Ken Dembny