[Gooserider]

Never seen that pump so I can't advise you on the mod, but the loop question is easy...

Think about the old experiment from grade school science with the inverted glass in a bucket of water. As long as the open end of the glass stayed underwater, the water in the glass stayed in it. (or a hamster bottle)

Same deal with your res, as long as the pump inlet and the loop return outlet are below water, the water will stay in the loop, no problem. You can even take the cap off and add coolant.

Filling might or might not be easy, depending on the setup. If the pump sucks enough of a vortex to pull in air from the cap area, or the return is splashy enough to be a problem, then filling with the pump running won't work. In that case, I would fill the res, cap it, and run the pump just long enough to get some of the coolant into the loop, then turn it off; uncap and add more cooolant. Repeat as many times as needed to fill the system and get the trapped air out.

If you don't have vortex or splash problems it's easier. Fill the res, turn the pump on, and just keep adding coolant until the loop is full and all the air is out.

Gooserider