I was just reviewing a file that had the material for elbows defined differently than the straight pipe. Turns out both could be the same material. I edited it by going to the material list and deleting anything in red so that the first material definition carried through the model. The run had lots of twist and turns so it was kind of time consuming. Is there a faster way to do this?

You can do in graphic mode. Activate the icon materials, it will show the materials used on the upper right corner. You can change there thematerial globally

I clicked on the material icon and it brought up the legend. I then double clicked on the material I wanted to change but it said, "Value edit is disabled for this input property."

My bad. Sorry. I didn't check. It shouldn't be. I can not see the reason.
Some values can be globally changed this way.

Try using the "Material List".