I’ve only ever used meshlab for file format conversion or holistic mesh based things such as decreasing the number of faces (decimation) and converting triangular faces to quads. I’m not sure if there are modelling type tools in there. I’d be more inclined to go into blender in order to move / extrude faces, especially as you’re working with jewellery models. Why not use Rhino (presuming your file conversion question above meant that you’re a whizz on Rhino?)