yes, pretty much. Measure the width and height of the opening, but bear in mind that the current unit most likely overlaps the edges by a quarter inch or so.

Then look at the size specs of the new unit(s) you are looking at. Widths are somewhat standard so height may be an issue. Look at the installation specs.

If the new one is shorter, then all that is needed is to put something in the bottom to raise the new unit up. A handy man can do this. But if it is taller, you may need a new cabinet depending on your situation.

We just replaced a microwave/single oven unit with a double oven. We talked with our general contractor before ordering to make certain we could do it. We pulled the specifications for the new unit and we all measured several times. He was able to fit the double oven into the space by opening the existing space. We were fortunate that we didn't have to lose any space from the cabinet above the unit, or the drawer below.

I agree with txjoyce-meet with your contractor first before ordering any applicance-"measure twice & cut once!"
I am in the exact situation-be sure your contractor can install considering existing cut-out & electric & weight of product to be installed.