I'm not sure exactly what that red handled valve is, but what it ISN'T is a ball valve. I doubt that it's capable of isolating the tank, since it's hooked up to both the boiler (which isn't isolated), and the system plumbing (which isn't isolated.)
There is usually other valves in the near-boiler plumbing to be able to isolate at least some of it so that you don't need to drain down the system to work on things, but your pictures are less than complete.
BTW: BadgerBoilerMN has it right- looking at the orientation of the shiny-new pump, it's pumping toward the expansion tank, not away, which can reduce the lifespan of the pump. Whomever replaced the pump SHOULD have corrected the near-boiler plumbing, but as a quick swap on a tight budget that error may have been ignored (assuming they had a clue in the first place, which isn't always a good assumption.) DON'T just flip the pump around when swapping the tank, since that would screw up the boiler, and boiler efficiency, which is designed with a preferred direction of flow.
When re-plumbing, make sure that the pump is in a straight line from the pipe from the air-scoop/expansion tank, not pulling against a right angle turn. The turn in the plumbing induces turbulence, which increases the amount of cavitation at the pump impeller, reducing pump life. You'll get better flow and longevity out of it if you follow a few simple rules.