limited options that i can think of...

1- write a logic in akamai to add system prompt (add or overwrite the system prompt from client side). similar to this example, just add some js logics to change request body json. https://techdocs.akamai.com/edgeworkers/docs/transform-response-content

2- if akamai can't do that, Azure API Management can definitely change request body. but some extra $$$