Locally refine hex-mesh based on spatial coordinates

[niklassay]

Hey Neper-community,

I'm currently using NEPER for my PhD and want to generate microstructures with a void in them. I've already created a prototype mesh using python and a simple element deletion in postprocessing. In the postprocessing, I determine whether a node lies in the specified ellipsoid based on its nodal coordinates. If yes, I append it to a list of nodes that will be deleted in the next step. However, as I'm using a hex-mesh, my chosen voxel size still leads to a quite blocky approximation of what should be an ellipsoid. Therefore, I want to locally refine my mesh in an area slightly larger then the ellipsoid before I do the element deletion.
For the last two days I tried to find a solution to this seemingly trivial problem. I imagine that the least tedious way would be to do it directly in NEPER, as I wouldn't have to fiddle around with the grain definitions and element sets in postprocessing.
Is there a way to specify different mesh sizes for different spatial coordinates during NEPERs -M call? If not, does anyone have an elegant solution in mind to refine the mesh in postprocessing, e.g. using gmsh?

Thank you in advance!
Niklas