Usage analysis is global and therefore not attached to a particular program point. Only localized warning can be disabled using @warning.
A first question is why you would want to disable this warning: it seems indeed to be a valid thing to warn about. (If the constructor is exported through the .mli, then no warning will be emitted.)
One valid case where one wants to silence the warning is if values of these types are only built by a C program on the other side of an OCaml/C FFI. Then a valid way to disable the warning is:
let _ = function
| Known_location (a, b, c, d, e) -> Kown_location (a, b, c, d ,e)