If you don't control the code and are modifying it to do an in-service upgrade of a running binary, then this is a special situation: you're shooting a 2016 re-make of MacGyver targeted at a geek/programmer audience.

If you're Red Hat and you do have the source, but the service cannot be stopped, and yet it must be upgraded, yet you didn't plan this into the software (and yet you didn't write in it in Lisp which could save your ass here) then you're plain stupid. If you're stupid, you're not going to pull off this highly technical, intricate hack, that is looming with pitfalls.