Manipulating facial musculature surgically?

You raise an interesting point. The variations in facial expressions can indeed be attributed to a combination of factors, including muscle insertions and nerve control. While the basic muscle structure is consistent, the way those muscles are controlled by nerves can differ among individuals.
In some cases, certain facial muscles might be selectively modified by reducing or rerouting nerve input (called a selective neurectomy). This involves targeting specific nerves that control muscles responsible for particular expressions. This approach allows for more precise control over facial movement while preserving natural expressions. Additionally, for muscles like the DAO and platysma, there is potential for reduction or removal, although this is less commonly performed due to its unpredictability.