Change hardcoded value in executable-Collection of common programming errors

You still can use hex editor in order to change the hard coded constant.

Another way is to use debug api, provided by any decent OS. In Windows it is WriteProcessMemory function.

It looks following way – the launch application runs the modified application in debug mode. Changes needed constant and then runs it.

Of course, the modified application may use anti debugging techniques – in this case the solution is not trivial.

In both cases, you have to know where this value resides in the memory (executable file). This way some reverse engineering have to be provided.

Note, after the last question edits: All this answer is for native executable files. For managed code it probably is more complex.