Can small block oil pump be replaced without pulling the engine?

The trick is turning the crank to get the counter-weights and rod throws to give max wiggle-room/clearance when removing/installing the pan.
Don't rtv the chit outta it, or it'll leak worse.
Contact cement (3M weatherstrip adhesive) to hold the side gaskets in place, and 4 pea-sized dabs of RightStuff prefered, but rtv has been known to work, only where the end and side gaskets meet.

Why are you replacing the pump ?