Question: How can i refresh grid data when new data added in exts?

Answer: 
Making it const and making it static do two different things.

* if it is const, each function call gets its own unchangeable instance of the struct
* if it is static there is one changeable instance of the struct shared across all function calls

It sounds as though what you want is a struct instance that is both static and const, which is a reasonable thing to do.

Performance wise, the static version should have a slight edge, as construction of the struct instance will only be done once.
If you declare a variable static within a function it is only initialized once when the function is entered for the first time. If you declare it non-static it is initialized each time the function is entered.

In your case it can make a slight difference. With *static* the array will be allocated in the static storage and initialized no more than once. Without *static* it will be allocated on stack and each time the function is called.