The big thing to consider is -- how different will the layout of the structural frames between the two materials?
If the basic layout is essentially the same, I'd recommend continuing to work with the same Shared Grid system. Since it aligns with the architectural elements and the MEP is using it, this will generate the least amount of work. Often the biggest impact of changing materials is primarily resizing the structural elements -- but having them stay in the same place. And it's OK if some of the grid lines don't get used as you use the different material. Or if some of the new structural walls or columns land on different locations and don't land right on a grid line.
But, on the other hand, if the different material leads to an entirely different layout -- it might be easier to create a new system of Shared Grids.