How to add function pointer for wrapped library?

How does Box64 export global function pointer variables from wrapped libraries for usage by the x86 main program? Furthermore, when such global function pointer variables are modified either by the wrapped library itself or by the x86 main program, how is data consistency maintained? For example, after the wrapped library internally modifies a global function pointer variable, how can the x86 main program invoke the corresponding function via the updated function pointer? Are there any relevant reference examples implemented in Box64?