Modifying the mesh with shapekeys in any way is risky business. It’s worth a try to see if you can do it, but be sure to always save a version of the file before modifying the mesh.
Years ago when I used Maya changing the mesh would explode all my shapekeys (blendshapes in Maya) no matter what. But Blender can actually accept some changes. I can’t detect a pattern as to what ruins shapekeys or not. Small changes like adding an edge loop or combining separate objects is usually a safe change. But it’s a lottery; any mesh change can ruin SK’s.
