Final answer:
P&G's addition of vitamins to Pantene's formulas represents a product modification strategy. This entails alterations to the product's features to make it more appealing, unlike repositioning that changes consumer perception.
Step-by-step explanation:
When P&G added vitamins to its Pantene shampoo and conditioner formulas, it used product modification to revamp the brand.
Product modification is a marketing strategy that involves making changes to the existing product's features, quality, or style to make the product more attractive to the target market or to reach a new segment.
This strategy is different from brand personality, which reflects the brand's image and values, and market modification, which involves changing the structure or dynamics of the market itself.
Repositioning, on the other hand, could potentially be the answer if the focus was on changing the perception of the brand in the consumers' minds with a new proposition. However, as the addition of vitamins is a functional feature enhancement rather than a change in brand perception, product modification is the correct answer.