Does applying fenugreek paste on the breasts to enhance their size results in weight gain? Or is it absorbed by the breasts only?

No. Doesn't sound like a good idea. If someone discovered a harmless cream to apply to breasts and make them grow larger, that would be the talk of the world... For at least 20 years. But, fortunately, there is no such cream. However, ingredients in creams are absorbed into the skin, usually in small amounts. If large amounts of chemicals got through the skin, that could lead to medical side effects.